Thanks for your concern dlochner... you are right about condensation... but not about safety or expense.I would be very hesitant to use a portable unvented propane heater on a boat, for a number of reasons. Chief among them is expense, safety, and condensation.
Heat will be a critical issue on this trip. I should have known better than to post about Big Buddy/Little Buddy Heaters... it seems to rile people up, and that was not my intent. Please do yourself a favor and read up on them... they are amazing, reliable, economical on gas, and safe... the trick is to have adequate makeup air... condensation requires daily attention when it's cold out, not too big a price to pay for warmth. My real concern is the propane storage.... the bottle(s) will be in a bottom-vented cockpit locker with bulkheads, and NEVER the interior of the boat.