Cheap Poly Decking
Both of my catarafts have decks down the left side. The first was made out of urethane-coated plywood by AAA in Denver, and is heavy and pricey to have made, but works great. The second has a deck of trex-like material I bought at Lowe's. It comes in pieces of 12' X 8", works as well as the more expensive decking, only cost about $35. I just drilled holes for the camstraps used it textured side up, and was good to go. The only drawback is that it is more flexible than plywood, so your frame needs to support it better.
The stuff is easy to work with, and I like it so much I made a raft trailer out of on the frame of an old Toyota pickup!