Matt,
Urethane will adhere exceptionally well to any preped surface. Will not stick to things like waxed paper, polyethlene, etc. Gorilla glue is a one part urethane. Low density foams have no strucrural value but higher density foams can be as hard as a rock & very strong.
Tommy,
The density you'd want for the Sportsman would be 4 lb, which has more structural capacity than lower densities while still very good flotation quality.
Timmy,
Insulating a boat is like shoveling sand against the tide... Where most of the thermal transfer takes place is through the wetted surfaces of the hull. But if you were to try to apply foam to vertical and overhead surfaces, you want to spray it on. Like:
http://www.foampower.com/ I think that your efforts to do so would less than productive though...
Urethane foam isn't in itself flamable, but within a foam covered area, the foam will act as a reflector to heat and thereby intensify an internal fire very rapidly. Once the urethane does start to char & burn the fumes are exceptionally deadly. Code for foamed walls and ceilings in buildings require a barrier between the interior space & the foam, usually 1/2" sheet rock. The barrier keeps the foam from reflecting heat for a longer time, possibly allowing the fire to be extinguished. Un-shielded, urethane foam can intensify a small fire from 500 degrees to over 5,000 degrees in a matter of seconds. (see:
http://www.monolithic.com/foam/fire_hazard/index.html)
Br,
Patrick