Choice depends on the amount of camping you plan to do during the winter or wether you just want to take the chill of the air for those odd occaisions when the temp gets a bit low. I have a Rinnai 1.6Kw (very small and easy to stow) catalytic gas heater as I mainly rely on hook up during the winter but it is there if needed. Same as Windysurfer, never set the CO alarm off when I have used it, even after several hours of use. I wouldn't leave it on while I'm sleeping for the simple fact that the catalytic convertor will not function efficiently once gas pressure starts to fall and CO will be emitted (even though I have a CO alarm I wouldn't risk it). Temperature soons falls in a van and if you want to keep a comfortable temperature throughout the night whilst sleeping then you need a proper thermostatically controlled gas system installed.