Teardrops n Tiny Travel Trailers

I'm trying to maximize the 48" in height, so I and thinking of flooring my TD so that the only thing that is above the frame rails is the 1/2" or 3/4" plywood.
What I want to do is build the subfloor and insulation below the frame rails, so I will build boxes in between the cross tubes and attach these boxes to the inside of the 2x2 tubing. I will drill and tap (locktite of course) into the inside of the tubing, insulate these boxes and then lay the flooring on top and screw the flooring into the framing of the boxes.
I will also build a box in the floor for storage.

This will allow me to place the walls on top of the frame and screw into the sides of the flooring.

I am going to use Oak plywood for the sides (stained and varnished) and aluminum skin for the top. I will have trim (not sure what type) to cover the attaching screws.

That's similar to what I'm doing, but I'm not making boxes, just cutting insulation and placing it between the frame rails. There will be some heat transfer from the steel frame rails, but it shouldn't be an issue. Will probably add a sheet of plywood or alum under the frame to protect the insulation. If your cross members on the frame are on 24" centers, the 1/2 plywood is plenty for the floor.

In my TTT, I will be attaching my floor (3/4" since we will be standing on it) to the frame via carriage bolts through gussets welded to the frame, with construction cement between the floor and all of the steel rails and cross members. The 1/4" luan side skin will extend down the outside of the frame and attached to the floor via screws and glue to a strip of spruce, 1" high x 3/4" wide, which will also be glued and screwed to the plywood floor. The part of the side skin that extends down the side rail will also have construction cement to stick it to the steel. I've tested the floor by standing on it and even jumping up and down to see if it flexes, and it doesn't. I have no other supporting structure under the floor other than than the frame, and the spaces between supports is about 25" x 56". I thought about some center supports between the cross members, but not sure it's necessary. I may put them, but if I don't and it ever becomes necessary, they can be retrofitted in place by removing the insulation, welding them in, and reinsulating. I have frame andfloor photos if you want to see them.

Attached my walls to the floor the same way. You can see my 3/4" x 1 1/2" strips I used to attach to the wall and floor with glue and screws just as your diagram. Used the same method on the front and back walls. Used recessed carriage bolts per your diagram to secure the floor to the fame. Turned out rock solid.

I used a real generous bead of silicone glue on top of the trailer frame to help secure the floor to the frame and to eliminate creaking and prevent water from getting into the area between the frame members and bottom of the floor.

GeorgeT wrote:I used a real generous bead of silicone glue on top of the trailer frame to help secure the floor to the frame and to eliminate creaking and prevent water from getting into the area between the frame members and bottom of the floor.

Do you find the silicone glue in a tube? And, does Lowes or HD have it? I was thinking of using contractor grade liquid nails to do the same between the floor and frame and sides and frame.

It's been a while but I believe I got it at Home Depot in a large tube that fits in a caulking gun. The liquid nails oughta work just as well and I think it's not as expensive. If I had had some on hand at the time I probably would have used it instead and saved my slicone glue for another day. Either way.