Step 9: Attaching floor to frame
In my case I primed the floor, screwed it all together, and bolted it to the frame. One side note - there will be a gap between the metal crosspeices of the frame and the wooden subfloor. I used paint stir-sticks and construction adhesive to fill in that gap.
I countersunk holes in the top of the floor where carriage bolts pass through the floor to match up with the existing holes in the trailer.
Then I went back and bondo-ed the holes to get a smooth floor. Once that was done I used floor paint to paint the floor green. Some folks use linoleum, plastic tiles, etc. You can use pretty much whatever you want, being mindful of the weight.