Best way to frame a Super LIght Harbor Freight 5x9 floor

[yuppers]

Hello everyone, I'm a long time lurker first time poster because I'm not able to find an answer for this particular question anywhere, please feel free to link to a thread, I'm not very good at using the search function. Anyways, here's my question: I'm building a 5x9 HF squaredrop so I'm extending out 6" over both sides and building wheel wells over the tires as well as bolting a 1x5 foot subframe to the front of the trailer to support the front overhang. My plan is to do a 1.5"XPS sandwhich with 1/8" baltic birch laminated to both sides and the cross memebers shimmed to provide support. Will the sandwich floor be strong enough with just a perimeter frame or does there need to be 2x2 spars running widthwise to strengthen the cantilever?
If Spars are necessary should they be directly over the crossmembers or in between so the foam can be supported by the metal crossmembers?
Will be towing with a prius, hence the 1/8" ply.

[QueticoBill]

if the grain ran across the trailer, I think the sandwich panel will cantilever 6". I think I'd also seriously consider 3/16" (5mm) or 1/4" for top at least, though I like balanced panels.

[Pmullen503]

I made my floor the same way but I used width wise spars so I had a solid structure to bolt through. I used 1/4" ply over white expanded foam. The floor will flex where you kneel on it. I would use a denser extruded foam if I had it to do over.

I'd use the cross beams and denser foam, I think you'll be fine. I don't think you need to extend the frame. My foamy cantilevers 18" in front with no support!

[JasenC]

With Luane you'll need an extensive frame work, that stuff is to bendy. I'd step up to 1/2" ply both sides or 1/4" on the underside 1/2" on top. Frame it with 2x2's and plenty of glue and screws.

[QueticoBill]

I know 1/4" works, well adhered to foam core. Any of the flooring underlayment plywood products should work. I might go to 2" foam if cantilevered ovet the edges of the frame. Perimeter one by frame. Think airplane, not house.

[pchast]

You can make the web frame of 3/4"material on edge.... Airplane not house as stated....

Please experiment.

[noseoil]

Simple way to see would be to do a mock-up for the 6" overhang. 1X2's set on edge (1 1/2" depth for strength) should be plenty strong with an 1/8" ply skin glued (and nailed) to the frame & reinforced with foam. We did a similar frame for ours with 1/8" ply skins, but there was "0" overhang, so the frame was set with the 3/4" thickness laid flat on the frame rails. There is a small overhang at the front corners where the frame is tapered toward the hitch, but it's very small & not a concern.



The 1/8" material is plenty strong enough (Baltic Birch would be best here), but I did reinforce the area where your butt sits with another layer of 1/4" at the doors, as I felt the 1/8" was too thin to kneel on prior to the mattress being put in place. I was concerned that a knee cap could puncture the skin when building, so I used some 1/2" OSB during the build for stiffness. The 1/4" panel just covers where the doors are as the mattress helps spread the loading from sitting & sleeping pretty well, a "structural" mattress if you will.

I don't see a problem with the floor, just do a bit of thinking about how things are fastened, glued & joined to make a good stiff box which will last.

[Woodbutcher]

If you are using the 2 piece sidewall HF trailer, I took out two of the internal cross pieces and bridged the seam between the front and rear side rails, making them one long sturdy channel. I then moved the axle back 6 ". I could use one existing hole and only had to drill one more hole for the spring. The cross members were replaced with large angle iron to form up the deck. I ran my floor crosswise and seems it over one of the cross pieces.

[philpom]

Hopefully this helps, this is how I framed and mounted my floor deck to the harbor freight 4x8 frame. The cross members don't go all the way out to the edge but they could for added support if needed. They don't go all the way across the middle so I have room for running wires, pipes and tubing etc above the steel frame. My walls sit on top of the floor right at the edge, my camper is if I recall 64" wide.

[cuyeda]

If you are using the 2 piece sidewall HF trailer, I took out two of the internal cross pieces and bridged the seam between the front and rear side rails, making them one long sturdy channel. I then moved the axle back 6 ". I could use one existing hole and only had to drill one more hole for the spring. The cross members were replaced with large angle iron to form up the deck. I ran my floor crosswise and seems it over one of the cross pieces.

By any chance you would have photos for this modification?

Thank you

[philpom]

I built a 5x8 on a HBF 4x8 frame like this. The 2x3 line up with the cross members of the trailer frame.





It's 3/4" BCX, then framed in the wheel wells and laid in 1.5" pink foam board and 1/2" gym flooring directly over it. The wiring runs under all of it so easy to access and add plus it's easy on the knees. The queen bed goes directly over the the floor and wheel wells are flush. Rock solid, my tiny camper weighs under 900lbs dry.