This is a big job. Had a 2007 Zepplin. Water damage in the bedroom. Had to replace floor. Top layer 3/16 plywood/ then 1.5" foam/ then 1/8" bottom, which was plywood too! There was no sub structure, only the plastic wrap that enclosed the bottom of the trailer and then the ground! I had to build a 2x2" frame and then put 1/8" tempered board on the bottom. Then bolt the frame to the few and far between aluminum cross members. Then "joist" the frame with more 2X2 and then put 1.5" foam insulation in and then cover the whole with 3/16 tempered fiber board top. Worked like a champ but I was truly astonished when I first removed the linoleum. Had no idea. I think preventing moisture condensation is crucial in a TT.
Oak