I have two Coleman Black Cat heaters aboard. We haven't done any long-term cold weather sailing, but if I did I'd want a vented-ducted system to get the condensation out. Also I think hydronic is an easier install because it's easier to run coolant hoses than much bigger diameter air ducts, but hydronic is less 12v power-efficient.

We do have a CO alarm aboard and it never triggered, so I think these things are fairly safe. However we never go to sleep with it on, rather we sleep in sweats and add blankets. Last Fall we were out in several overnight lows in the low-40's and it was nice to fire up the heater while the water heated for morning coffee. It definitely took the chill off.

I've struggled with the same installation/cost barrier and for our current use it's not worth it (for now) to go the Espar or Wallas route. Another option would be to extend the galley gas line with a "T" connection and install a propane bulkhead mount, but I don't have bulkhead space I'd want to spare for that, and the Admiral thinks it looks "intrusive" for the amount of use we'd actually get. She says the Coleman heaters are "good enough" for now, and if I want go where we really need something more she's heading in the opposite direction (south) and I "can come visit" .

BTW -- plain old PVC pipe from Home Depot makes a nice deck storage tube for extra gas canisters. A few end-caps, a 1/8" vent hole in the bottom and an L-shaped piece of aluminum 1/2"w x 1/8" thick bar stock hooked below the bottom gas cylinder let's you lift up the stack. Attach the tube to your stern rail with tie-wraps or hose clamps. The writing wipes off using Interlux 202 solvent wash.