An amphibious craft must, of course, float. Unless it’s a submarine.
We’ve been scouring the interwebs looking for cheap, decent things to use as flotation: inflatable pontoons, fold-up coroplas boats, Dacron (R) skinned floats, or fiberglas and foam construction… the list does go on. Our biggest concern? Re-inventing the… well, not the wheel, but the pontoon… while spending more time and money than just buying a set of the things. Right now we are experimenting with sewing abrasion resistant covers for pool toys.