Fresh new slate, build ideas

[Projector]

Ok, so I've got this.

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Now what?
Contemplating an overland style rig, even though won't be doing anything beyond dirt roads, which can be anything from gravelly smooth to rocky rutted with ditches.
Box truck square simple.

Wondering if a foamie is advantageous with dimensions of 7*12*7. Concern of course is roof span strength , body flex/cracks and stress/torsion during travel as well as difficulty and time to build vs traditional frame+ply. Looking at a surface area of approx 350ft², 7*12 roof span. In other words, almost triple the surface area andof a 4*8 teardrop and double the span. 3x time to build?

Having read ghcoe's excellent build thread, where and how to reinforce roof/sides from flex/stress/deflection as well as time to lay all those layers/ coatings are my initial concerns.

Realize that similar to architecture reinforcement, trusses, spars and ribs are required. But what and where, strong enough yet light enough, xps or wood reinforcement, etc... The million and one details of assembly techniques.
Anyone know of any links, comparables?

I've got ideas like center length roof rib, cross roof trusses, corner angles, floor to roof inner walls and cabinets to box and support, triangular corner trusses, multiple cross directional cloth layers, etc...
Probably all boat building skills for which, being a landlubber, I have zero knowledge.
Being in the pre-planning stage, considerations and design is where it's at now. Time to build and cost are the major considerations. Not sure in my mind if the extra time and weight saving of foam is a gain over traditional frame+ ply. Know I can build this in frame and ply, gauging the value and worthiness of foamie light!

Any and all comments are appreciated.

PS, being new, not sure if this is the best thread location. Please relocate if required. Thx.

[Projector]

I've read Seanc foamie truck camper build which is close.
Not sure if strong enough.
Fyi
viewtopic.php?t=64361#p1145004

Idacamper build
http://www.idacamper.com/the-prototype/

And there are others out there if you Google carbon fiber slide in, etc...

[aggie79]

What a cool platform! I look forward to your design and build.

[Projector]

Maybe I need to ask a specfic question on my bed mounted ttt?
Any suggestions on supporting a 7x12 roof span
of 2" XPS?
What type of reinforcement and where?
Lightest and or most cost efficient?

Possible options might be;
1. Ply sandwich, what thickness ply?
2. Thicker TBII coat, maybe double cloth?
3. Lattice grid of reinforcing cloth/TBII?
4. Stud ribs, 2x2 or 2x3?
5. Floor to ceiling panel walls every 3ft?
6. Hybrid roof trusses
7. Corner triangle braces
8. Combinations
Other?

Imho, the increased span, weight and size of the box requires more adhesion strength in the corners and further roof support due to the increased stresses. Would definitely double up on glued surface area by adding 2x2 xps edge strips for more glue holding power.

How to do it is the question that I am looking for insight from the experienced on here. It would be greatly appreciated.

[noseoil]

I would think about using some "formed" beams (ribs) for the roof system, not necessarily a truss. With a truss I think in terms of a bottom chord, top chord & some type of webbing between them for loading (like an "I" beam). You can do something similar to a boat cabin roof, with cambered beams made in a form, use strips of wood bent & glued together.

A 2 1/2" deep beam 3/4" thick with 1/2" of camber would probably work well enough, but I would test one with a load on top to see how much deflection you get with a weight system you can add as you go. You might be able to go smaller than 2 1/2", maybe only 2". Just make a simple form with the arc drawn on a sheet of plywood for the length of the beam (roof span) & add blocking to it along the line for the clamps to press things in place & use a "pin tacker" to set things up with when you're gluing. Use waxed paper or paste wax for a mold release so the beam doesn't stick to the plywood. Take the finished beam, pin the ends to simulate the wall joint & start adding milk jugs of water to see how much weight it will support. Once you decide it has enough load & is starting to deflect, figure out the total roof load, divide by the weight supported on that one beam & that will tell you how many members you need to have for the support. You might end up with 12" on center, 16" or 19.2" that works out for the load. Then you can put 2" foam between the beams & have a strong, light structure.

I know this sounds like a lot of work, but time is free, right? 3/4" or 1" rippings about 1/2" thick would bend easily over that length & glue to be plenty strong, like a glu-lam beam only smaller & lighter.

[pchast]

Just talking but...

How about using sheetmetal channels the height of your xps at every joint. even use 2 opposed. Or if the panels are too wide cut them in half and do the same thing for a light composite. One of the people on the panel used a caulk to glue such on below the PMF.

[Pmullen503]

7 ft tall walls on top of a bed that's already 3 ft off the ground? Maybe a lifting roof style to keep your driving height down.

[Projector]

Thx for the responses all.
@Noseoil - laminated support beams are an excellent option that would be light and strong. Great suggestion to determine total required.
@pchast - used the sheet metal studs before and love the lightness. Might have to revisit them to determine deflection with load along it's side length.
@pmullen503 - the height was just an approximation at this stage. Yes, getting near 10' overall height but not different than today's slide ins, fifth wheel and class c. Point is taken though, how low to go?
And at 7*12, raised roof with reinforcement, weight and size are considerations. What or how to raise and lower? Love the idea for a lower roofline.

[Projector]

So I have been going through the thought and planning process , thinking about the possibilities.

1. Wood and ply build. Quick, simple and heavy. Initial calculation around $3.50/ft2 for walls, roof, insulation and paint. Long term durability questionable of course but would figure to properly paint all wood sides and have a roof with extensions to keep rain off roof/ wall joint and walls. And replaceable for future making it easy and cheap to do so. Would keep lifespan of RV section inline with vehicle. Why build a 40 yr RV section if the mechanical only lasts 20 yrs?

2. Glued Metal frames and walls, utilizing metal studs and 30ga flashing. Also around $3.50/ft2, thus same as wood. Lighter and more durable but unproven technique. Polyurethane glued metal studs and walls be up to the task?

3. PMF Foamie with frame. Love the simplicity of this from an engineering and design standpoint but not so great on build time and method. How to properly lay the canvas on a 7*14 roof span with my short arm span and load bearing on the roof to do so? Possibly assemble roof and coat while on the ground and install in one preformed piece. As well, the cost to do so could be almost double in cost and time. XPS is $40 a 4*8 2" sheet here making it about $5.00/ft2.

Drew up a sketch to see if my proportions look reasonable. One is straight box, the other lowered sides like a lazy days to give a sleeker ground hugging look just for fun. Also give the option of below deck storage.
Looking to commence Nov1 so roughly three weeks to finalize.
The look/size is roughly like a Chinook class B on this chassis

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[Projector]

Also been thinking of a name and style.
The overall cab design reminds me of locomotive proportions and maybe using a classic streamliner coach car interior design and style thus a name like TransWestern Express. And it is a Chevy Express after all.

Another thought that comes to mind is along an expedition rig, Terra6 is a thought since it does have the
6l LS V8. Build it overland rugged design and colors.

[Projector]

Anybody know what this means?
Thunderbirds are go!
Won't let me post pics.
And constantly tells me to login.
Admin, help! Lol

[KennethW]

Why all squared off? Why not radius the whole roof and back?(a radius is a lot stronger) Slope up from the cab and round the back for air flow. By doing that(with 2" foam) you can get by with maybe three cross pipes under the roof. A 3/4 gap between the tubes and the roof make's for a great place to hang stuff.

[Projector]

Squared off for a couple reasons.
1. Simplicity of build and strength, torsion box
2. Style matches cab
3. Going for the overland expedition look. I call it overland lite.

[Projector]

So I have built the box, PMF it and now have a foamie that I've driven 6 hrs on the highway and didn't leave a trail of polystyrene in my wake. Still have a complete box too and waterproof through a 2" rain day. Yay
But I can't seem to post any pics of my build without it saying I need to be logged in first before I can post and then being asked to login again and again.
Anyone have any ideas or admin help?
Would love to share it with all.

[KennethW]

So I have built the box, PMF it and now have a foamie that I've driven 6 hrs on the highway and didn't leave a trail of polystyrene in my wake. Still have a complete box too and waterproof through a 2" rain day. Yay
But I can't seem to post any pics of my build without it saying I need to be logged in first before I can post and then being asked to login again and again.
Anyone have any ideas or admin help?
Would love to share it with all.

Pics? Download Tapatalk on your Phone It makes it very easy to post pictures.