I've had a marine plywood floor for years. 3/4 inch, outside edge is rounded with router, 1 1/2 inch strap holes are rounded with router. I used a marine grade spar varnish, dilute first coat 25% with thinner., apply 3-4coats. The floor is narrow enough so when it hangs with weight it rarely has the opportunity to hit the interior tubes. I think your foam wrapping will not last and become a never ending source of trash you'll have to deal with as it unravels. No need for the floor to be too wide, I contact cemented a piece of durable rubber pad on the floor where the cock pit area is or you can screw on a small piece of diamond plate aluminum. While your at it how about making some running boards for the top rails. Better to walk on and a good base for rigging smaller items.