It depends on how much heat you're looking for. If you're planning on doing any winter / snow camping, I don't think any of the commercially available propane heaters are going to do much good. You see, they all have carbon monoxide cut off switches.
I tried using a lil buddy propane catalytic heater in my RTT and it would only stay lit about 2 minutes before shutting off.
To keep it lit, I had to open a window which let out any heat the unit was producing. Fortunately, I had sufficient clothing (layers) and a good sleeping bag so made do without the heater (-5F night)
I've found that a low watt hairdryer (300W) can kind of do the trick just to get rid of the cold first thing in the AM but really, for cold weather camping (<30F) best seems to be dress warmly (layers, balaclava, gloves).
BTW: A zippo handwarmer works wonders and will keep your feet warm all night if you throw it in your sleeping bag by your feet.
