Building the frame (like everything so far lol) turned out to be more of a project than I anticipated.
Sizing the wood:
I didn't want to add too much height to the teardrop by framing up the trailer - so I lowered the fenders a bit and ripped 2x4s down to something like 3" or 2.75" I don't remember off hand.
Half-lap joints:
I wanted to use half lap joints for the cross-members so every member was continuous. I used a router and little jig I made to cut out the voids. These were tough for me to get exact as I'm a novice woodworker, but they turned out ok. I used a Kreg jig to drill pocket holes for the screws to secure the frame together.


Bolting down: I used carraige bolts to bolt the frame to the trailer, but ran into an issue with using nylock nuts. They would strip out the square head from the wood when turning them. I ended up getting non-nylock nuts, using a lock washer and thread locker for security. (I'm open to thoughts on this approach)
Sealing the bottom:
I decided to line the bottom with 2 sheets of coroplast. I sealed everything with caulk - I'm hoping this will be sufficient waterproofing. I'm also eager to hear peoples thoughts on this approach (not that I can back out of it now though haha).

Insulation:
Because the frame is so tall, I went with 1" rigid foam insulation, cut it to size and filled in the gaps with spray foam insulation. I left a small gap between the top of the insulation and the floor - after reading more things recently, I'm nervous this space will cause condensation and then rot - thoughts?

I added more cross-members because I wanted more stability for the plywood above.

Floor:
I used 1/2" maple plywood for the floor. This part was straightforward - I glued it and screwed it to the frame.
