Hi Eric – thanks for joining 🙂
I’ll answer the part here that wasn’t covered in the whitewater topic.
You could definitely add a second layer of fabric to the inside bottom of an inflatable floor – you would just have to cut “windows” in it so the top layer of the floor could be attached to the bottom layer (either using baffles, or by joining them directly, as discussed elsewhere). The inner layer would also have to be cut smaller than the bottom and top floor pieces to allow them to be sealed together around the perimeter of the floor. All in all, this wouldn’t be too hard to do.
For reinforcing the tubes by laminating fabric up the outside of the tubes, that could either be done by adding separate pieces butted up against the regular floor piece, or by cutting a new, larger floor piece from a 2-3 m length of fabric (depending on how far up the tubes you want it to wrap). To get the correct shape, just lay out a regular floor piece and tube pieces on top of the 2-3 m piece of fabric (tube pieces lined up correctly between the dots on the floor and taped in place), and then trace around the resulting shape as far up the tube pieces as you like. Then subtract about 1 cm around the edges of the tube reinforcement flaps on the new big floor piece (so the seam strips will be able to attach to the regular tube pieces) and cut out the new, larger floor piece. That will be your bottom floor piece, and then you can add a double or triple layer inflatable floor as described above.