Join Date: Jan 2007
Location: N. Strabane PA (South of Pittsburgh)
Nice set up!!!
I agree with Terry Q the problem is coming from the concrete slab so you need a vapor barrier. Plastic sheet would be thin and I think you would eventually would wear holes in it over time. I would use two, maybe 3 layers of 30lb roofing felt or 3 or 4 layers 15lb laid in opposite directions. It would provide a little bit of cushion and grip for the ply. You could paint a sealer like Red Guard on the concrete in addition to the roofing felt if you want to but I think that would be way overkill. Be sure to seal/finish the plywood on all 6 sides.
I would also run some Tapcons right into the concrete unless this is something you pick up once in a while.