I have been using the MR Heater, Big Buddy, it works great and I have not had any problems with using it. I have a power adaptor the plugs into the power outlet that will run the fan, if needed, so I don't have to use all those dry cell. I think I have enough air leaks to meet their ventilation needs. IMHO, I think most MH leak enough air to take care of the oxygen needs. Just check you CO & fire monitor.
As soon as you get the heater, BEFORE you use it, get the manual out and READ it, then FOLLOW the instructions. Especially the instructions regarding required ventilation.
If you follow the instructions very carefully, you will be safe.
If you fail to follow the instructions, you could DIE!
READ AND FOLLOW THE SAFETY INSTRUCTIONS! YES, I AM YELLING, IT IS THAT IMPORTANT!
CM1, USN (RET)
2002 Fleetwood Southwind 32V, Ford V10
Toad: 2006 Jeep Rubicon LJ
Other toad: '06 PT Cruiser, Kar Kaddy dolly
Toy: 1977 Dodge W100 CC SWB, 3/4 ton axles & springs
"When seconds count, help is only minutes away!"
We've been using Mr.Buddy for ~2 years while boondocking and been very happy with it. We always make sure to ventilate properly (usually crack open a window and turn on the roof fan), plus we never use it while sleeping or unmonitored, but it's been perfect for keeping the rig warm in chilly AMs or PMs.
I use a different type heater in my coach that does not require ventilation. Heating my coach in the winter and having to open a window or vent does not make since to me. I want my heat to stay in the coach! As you know heat rises and will go right out of a window or vent. I stay away from heating devices that may have ventilation issues don't want to risk it, not worth it to me.
The Big Buddy asside from being double the BTU output 18,000 btu rather than 9,000 btu has a couple of positive features that may influence the decision on what one to buy and one negative although a small one. The negative is it is physically quite a bit bigger. On the plus side it has a built in fan that can be run on four D size batteries that fit in the back or a plug in the back cord and 120v wall wart. Or a 12v to 6v voltage reducer from Radio Shack you can make up easily. The other advantage is it has a low pressure quick disconnect fitting preinstalled to run on low pressure propane instead of high pressure like I do coming right off of the coach tank. Some folks are paranoid about having the high pressure propane specific hose run into the coach. I am not. We use the smaller one as it is more than enough btu's on high to drive is out when it is near freezing in a 40' coach and it takes up less space. The little green one pound tanks will last 5-6 hours on the 4,000 BTU low setting. My setup will run about a month on low.
Surprised no one has mentioned that one of the products of combustion of these things is H2O.
I have one and use it on low, occasionally. Calculated the window opening I'd need from their users manual and with that open, and the ceiling vent open, I can't run it very long or it'll drive me out of the rig (330 sq ft). Have to open the door for short periods sometimes. This has prevented me from ever using it at night while asleep.
Then there is the sweat covering most all the windows, appliances, mirrors, the moist furniture, etc. Don't care for that but I can put up with it for short periods.
Of course it all depends on outside temp and local weather conditions. I still have it and won't part with it, just in case. BTW, I have dual paned windows. I bought the smallest one I could find at the time, I wish I'd been able to find a smaller BTU output unit back then. I have the Mr. Heater 4,000/9,000 BTU.