While these types of heaters can be used safely they often are not.
Next to portable generators, LP fueled portable heaters (a whole other subject for Darwin awards) are one of the highest number of deaths, by category, according to the CPSC due to CO poisoning.
One of the main dangers of propane CO poisionings is that when propane runs low on oxygen, for combustion, you usually don't know it. With wood, coal, diesel etc. the appliance will become sooty and you'll smell the poor combustion. With LP gas you don't notice it until it is too late and you don't wake up.
Also these heaters do not meet any of the marine safety standards for boats which makes using them technically against any of the accepted marine safety standards.
I have and do use them but I am very, very careful in their use.
These are my own rules for safe use:
#1 Propane bottles are only every removed and installed ABOVE DECK.
#2 Heater is ALWAYS lit and pre-heated above deck then carefully placed where it goes. Our heater is never, ever lit below deck. I ensure its operation above deck and only move it below when the ceramic has totally pre-heated.
#3 NEVER sleep with these units running
#4 Boat MUST be ventilated while heater is in use.
#5 NEVER place heater near combustibles or where it could tip over.
#6 Use non-slip pad under the heater
#7 ALWAYS use a CO and smoke detector with these heaters.
#8 ALWAYS be sure the LPG safety alarm is working (I test ours about three times per season).
#9 Assign only ONE individual to the operation and use of the heater, perhaps two if both well trained in lighting and extinguishing.
#10 ALWAYS pay attention to the flame and "noise" of the heater and shut it OFF before it runs out of LP.
#11 Always use fresh new propane bottles. I DO NOT believe in refilling the 1 pounders. I have seen far to many of them leak once disconnected. In my opinion these are one time use valves. We now leave our BBQ grill regulator attached to the bottle & grill between uses due to leaking 1 pounders after unscrewing them. There is NO good place on a boat for a leaking propane bottle.... Once we pierce the bottle it gets used and then recycled. If leaking when removed from the grill or a heater it gets immediately tossed into the dinghy.
We no longer use a Mr. Buddy on-board as we simply don't feel they are a safe enough appliance for our family. They can work great, but do make the boat rather moist, a nasty feature of a non-sealed combustion appliance...
Please, be very careful in their use...