: I still would not recommend using expanding foam. Expanding foam can create a
: LOT of force and if you misjudge the amount to use, you're likely to split
: your boat open.

This is only true if the foam is installed in a closed space (i.e., bulkheaded bow or stern) and you miscalculate the volume. Both my boats have expanded foam in both ends, installed before the bulkheads. The chemical reaction generates low temperatures and pressures, and there were no adverse consequences on either boat. These boats were built for my under-10 kids, and the peace of mind provided by the passive floatation is a valuable commodity to concerned dad.