Re: Flotation Compartments
I built a hollow sit-on-top kayak a few years ago. it has a hatched storage chamber then the rest is sealed compartments. The first time I used it I pooped the hatch after it had been in rather cold water then warm sun. The hatch almost blew open due to expansive air inside. I then put the tiniest hole in the hatch, with a heated up sewing needle backed by glued on rubber with a similar hole. That worked great as a pressure release. There are ones you can buy, but I enjoy making things with what I have sometimes.
Between the storage chamber and the sealed chambers. I glued in small plastic water bottle cap's threaded base, so I can then screw the cap on. Popped another sewing needle hole in the bottle cap. This micro pined bottle cap works as a pressure release valve when closed. And an air port when taken off, when not in use. I have been very happy with these. And they are basically free. And if I were to loose a cap, I can just buy a drink and have another one.
I would not fill with foam, don't lke the weight or potential moisture. If you put hatches on be very careful they don't fail when you most need the floatation.
"Yeah, well, that's just, like your opinion man"
-The Dude-