: That was one of the main things I was wondering; if it will hold
: together enough to assemble is it likely to be fine in use? If
: the skin supports it from the outside it might be able to hold
: up ok. I might try to increase the size of the stringers just in
: case.

The only concern, once the skin is on, is crunching into something with the boat. Your stringers might not be so tough in that case.
As for increasing the size, well, I probably wouldn't worry too much about that. Pine is already stronger than Western Red Cedar, and heavier . . . .
Plenty of boats have been built with lesser scantlings and do fine - check out the late Platt Monfort's "Airolite" boats!