Harbor Freight trailer and rough roads but not off road.

[hiker]

I have the Harbor Freight 11720# trailer and am planning on going off paved roads. If you are familiar with the Forest Service roads thru Dolly Sods in WV or the Green Ridge State Forest in MD. That about as tough as I would be taking the trailer. I may have to remove the housing to use it as utility trailer. So this is what I am thinking .
top to bottom
48" ply wall sandwich including 2" roof/ceiling sandwich.
1/2" ply 5x8 floor
1.5" 2x4 laid flat and longitudinal on the trailer.
3.5" 2x4 laid on end, framed out to 5x8, these be perpendicular.
1/2" ply 4x8
3.5" red frame
Riding indefinitely on the stock 12" tires.

My current thoughts bring it around 72" total height.

And your thoughts?

[Roly Nelson]

Hi Hiker, welcome to the forum. I have read your post, and am a bit confused about how you plan to build on a 4 ft wide trailer, yet your rig will be 5 ft wide. Is an 11720 HF trailer 5 ft wide? I have built 4 teardrops on HF trailer frames, never had a bit of trouble with them, always repack bearings prior to a long trip, have never had the much-feared problems with the 12 inch Chinese wheels and tires, but have never taken them off road, (except when I back into the campsite, adjacent to the paved road). Good luck on your build, perhaps you could offer some added info, and if so, I'll respond to it as well. As an aside, I feel 2x4 floor construction is way over-building, but that's just my 2 cents.
Roly, the li'l ol' So Calif woody builder

[hiker]

Hello,
I labeled each layer to help explain my thinking.

layer D 1/2" ply 5x8 floor
layer C 1.5" 2x4 laid flat and longitudinal on the trailer.
layer B 3.5" 2x4 laid on end, framed out to 5x8, these be perpendicular.
layer A 1/2" ply 4x8
3.5" Harbor Freight 1720# red frame

Layer A is bolted to the top of the Harbor Freight frame using galvanized hardware and blue locktite.
Layer B is screwed and glued to layer A, these pieces are 2x4 measuring 64" long. Laid crosswise on trailer, this provides the 5' width, i rounded.
Layer C is screwed and glued to layer B, these pieces are 2x4 measuring 96" long. Laid lengthwise on the trailer, this gives me 8' length.
Layer D is screwed and glued to layer C, 3 pieces of 1/2" plywood, the first two pieces are cut 48x64, the last is 12x48. layer c parts are under the seams.

Reasoning for the layers B and C is the required height to clear the fenders and that provides storage space with framing for under floor storage space roughly 12x12" boxes (I left my plans at work).

I googled some roads and found this clip from a ford in Green Ridge http://www.youtube.com/watch?v=nUoFmNWIN0E

[Modstock]

I do a lot of Off-roadin and have taken my 4x8 HF tear on rough dirt roads. Whenever I hit dirt I air my tires down to about 18psi plus or minus (depends on the terrain) . It makes the ride softer but I bring a small air-compressor to air back up.
When I take the tear more than a mile on dirt I air it down to 20psi . I also pulled the lower leaf out of each side since HF trailers are kinda stiff. Every year I usually go around and tighten bolts and screws up . Hope that helped.

[working on it]

I have the Harbor Freight 1720# trailer and am planning on going off paved roads. I may have to remove the housing to use it as utility trailer.

If you plan to remove the cabin, are you going to slide it on and off the frame? or might you mount rollers underneath, and use a winch? The roller mounted cabin could be secured with tie-downs and ratchet straps at each corner, for cinching tight for travel (easily double-checked before off-roading), and easily removed to pull off for utility trailer use. I thought of doing that, using heavy 4x4s as runners over boat keel rollers, and secured using locking pins and ratcheting car-hauler straps. But, I already have another trailer (car-hauler) for utility use, so I didn't pursue the idea. By the way, your post just has specs; no pictures or diagrams to illustrate. Could you show us a sketch?

[hiker]

I have my trusty graph paper but haven't learned any CAD programs.

I found this drawing on Google Sketchup, the my idea is a bit smaller, but similar shape and size.

72" high, 64"wide, 9' long.


rear view.

Still measuring my camping gear for compartment sizes.

[KCStudly]

Sounds over built to me.

You plan on filling in the perimeter gaps between the alternating layers of 2x4s and using the dead space (5 inches internal height) for storage? Not much useful space for a lot of extra weight in wood. Not sure if you are talking about drop down storage below the trailer frame, or just using the space between the plywood. Either way I would seriously consider using 1x boards on edge and not criss-crossing them; it's just wasted structure/added weight for the purpose of spacing. Think about it like building a structural box, not as if you are stacking a grid.

If the under floor storage is that important and you want to keep it above the trailer frame, I would consider using a 3/8 ply bottom, 1x10 perimeter frame on edge ("cheap" pine boards would do, I realize that they are more expensive than 2x4's, but you will need less of them and any left over can be cut to use for other things in the build) with two bulkhead/xmbr beams of same dimension, then 1/2 ply top deck. That would give you enough under floor space for your spare tire, camp chairs, extra shoes, pots and pans, whatever. Could even have enough space to justify making outside access doors to save the hassle of having to lift up the bedding to gain access. The bulkheads could even be made from 3/8 ply, but then you would want to use 1x corner blocking to stiffen the edges and give you something to screw (and glue) the joints together. Tho you might need a small portable step to get into the cabin comfortably and it would raise your overall height another 4-1/4 inches.

If you use lift up ply panels over openings in the top skin of the floor and 1/2 inch ply seems a little too flexible, just add a stiffening rib of 1x2 on edge under the panel.

Just my $.02, but it seems that so many people "default" to 2x4 construction. Pick the lumber that fits your design, don't let the lumber pick you, or your design.

Another thought to build a deeper under floor storage "unit construction box"; use 2x2's and build ladder frames (open frame trusses) for the xmbr's and rails, then box it all in with ply skins; 3/8 on bottom and side, and 1/2 on top deck.

[hiker]

Photos from today.

3/8" 4'x8' sub floor.


2x6" joists, this carries the floor out to 5x8', provides room for under floor storage, and clears fenders enough for larger tires in the future.

KCStudley, I wish I had seen you post earlier. I picked the lumber I am most familiar with. I was thinking its too much, so canceling the grid.

[rowerwet]

I built my tear with 2x4's going crosswise like you show, it was just wasted height and weight, both hurt when towing. I ended up ripping it all off the floor to reduce the height. my floor is just 3x8" ply on the overhang sections outside of the frame and two layers of 3x8" ply inside the frame.
box in the wheel wells to clear the wheels, you don't need the width for the bed down by your knees (where most wheel wells fall) and it makes the trailer shorter and easier to tow.
I store everything I need for camping in the bed when traveling, the mattress gets rolled up into the front. It still only takes a few min to set up at camp.
What I'm trying to say, raising the floor above the wheels make the trailer too tall, or the inside roof too short.