If you want to use a 110v heater while under way or on the hook, be advised that the power inverters can consume a battery very fast...and most alternators in the Yamahas have a hard time keeping up with all of the electronics we typically put on these boats.
I use a propane "Mr. Heater Buddy" when I need heat. It uses the little 2lb disposable bottles, which can be stored above deck, where any leak wouldn't end up in the closed cabin. It also has a tipover switch that cuts the fuel if it tips at too great an angle from vertical.
I've only used this heater a couple of times in Dec at the Ches. Bay Bridge Tunnel (CBBT) near Norfolk, VA. Both times, the heater was NOT run in the cabin, but up at the helm in the full enclosure. Purpose was to warm wet cold hands while fly fishing, so we could continue to fish. To keep the body warm, we fished in high-quality hunting gear.
If you ever use a fuel-driven heater in a cabin/enclosure, make sure you have a CO2 alarm. The little high-efficiency propane heaters are supposed to burn efficiently and not put out much CO2, but a malfunctioning one could kill you.