I used three sheets of 3/4 tongue and grovve plywood. I used the old floor as a template and placed the sheets crosswise, breaking them at the wheelwells. Also used asphalt roofing compound underneath to waterproof the ply. I tried icedam sheeting but would not stick to a horizontal upsidedown position. I'm gonna cove the ply with melamine strips when i put the steel runners back in as a spoil type board situation. i did the research on a full sheet of ply and a 500 dollar prictag was not worth it. I did 3 sheets of t and g for about 120 and im very happy with it plus it was way easier to install in sections. peace.
