I have been using them for 40+ years of live aboard (not continuous though) boating...like anything, wise use is different than less than thoughtful use that seems to get people in trouble.
There are all different kinds of space heaters, but ultimately to keep moisture down, it is just heated air that can keep moisture in the air versus forming on cooler surfaces.
I used space heaters in all my liveaboards and currently in my RVs.
I keep them on the low setting when absent....but still not for anything more than all day absences, and high when I am present to monitor it. I also never run a space heater if it is the only or only partial source of heat so that it's thermostat can keep it from running continuously. What that means is that if cold enough...I run multiple space heaters or another source of thermostatically controlled heat.
I buy better than minimal type space heaters with tip over, thermal and better construction than the cheaper models.
If you don't need quick heating or spot heating....or are space/weight limited, the oil filled radiator types are dang safe as long as mot run on high with minimal wiring supplying them. Again, running them continuous is never a good idea.
Having studied a fair amount of fire accident reports due to space heaters and extension cord/octopus outlet connections is pretty clear that continuous use or overloading is usually the fire issue, not the individual heater itself unless covered or too near a combustible source.
Are they the best at reducing moisture levels? No, plenty of other possibly safer methods...but if you need dry heat for comfort...they can be used with relative safety.
