I have made some custom Neoprene Cockpit covers before that kept a bunch of gear dry in a Topo Duo that was lashed to the back of a Raft that flipped on the Grand... All the other gear was damp or lost, but the stuff that was the deepest after the flip (in the boat though) stayed dry.
This would be a lot simpler than filling a boat with foam (PU foam tends to absorb water by the way). You could also reinforce the cockpit with a hard top just like on a sea kayak.
My approach anyway,
Originally Posted by riverrat
One of my friends wants to build a homemade fishing boat and use two older (river runner) kayaks for the pontoons and build the frame around them. Anybody have any ideas about this? or two older matching boats (color doesn't matter, just the model) that you need to get out of your yard/garage?