Yes, you will see it said that quite a few people do. However, really, it's a poor idea. Mr Buddy is a "Blue Flame" heater, and creates a measureable amount of carbon monoxide. Yes, people do die every year from carbon monoxide poisoning.
The Olympic Wave heaters are safer, but do create water and carbon DIOXIDE when they are working right. Deprive them of oxygen, which they use when they convert propane into heat, and they can create carbon monoxide, too. Or when the catalyst becomes poisoned. Safer, but still can kill you. There are some portable catalytic heaters. On here sleepy installed a "platCat" vented catalytic heater. It does use some electricity, but I would guess you could go a few days without charging. 
25 pages on good info and arguments!Afte researching it, I decided to upgrade my batteries and charging system and continue to use my noisy, constantly cycling, really annoying built in furnace.