Yes i have a little heater that runs of gas kicks out 1kw which is a lot in the back of a van it gets quite warm and as the van is vented so I don't get condensation, uses a tiny amount of gas something like 4p per night. Also the gas tank in a sealed box and is vented outside so should there be a leak it goes outside as propane falls as it heavier than air. The heater is above the tank level and mounted on checker plate and protected against anything being placed on it. works well but didn't want petrol vapours which is basically a gas as well in the mix so we removed the petrol tank and went gas only.
As you mentioned safety my gas tank is TUV and CE approved crash tested and is mounted on a frame that also is TUV and CE approved and can survive crush damage and in the event of fire has a blow off valve to realise the pressure with-out exploding.
So a quick question what certification does your petrol tank have?, I've seen marine fuel tanks, racing fuel cells and manufacturers own in-house made tanks on all sorts of truck mounts, nothing that wrong with any of them, just pointing out gas is sometimes more regulated than petrol and unlike petrol we use a big 110litre tank that lasts all week and is topped up weekly so we never run out, most importantly that means we don't have loose petrol cans or big jerry cans in the back of the vans which is where the real danger is, one falls over and you don't notice, maybe the tops not on tight, or the seals leaky, or your carbs leaking a little, you got vapour in your van add a heater with a thermostat with a bi-metallic strip and you have a spark as well when it make contact ( maybe 20-30 times a night) and you just warmed up the vapour making it more volatile to paraphrase an earlier quote " I wouldn't mess with petrol get it wrong and boom"
Saying that if you have electricy where you park your van just get a 200w IP rated heater ( the things you see in football changing rooms under the benches) there about £30 and get it wired in with a external socket and plug it in when you get home even easier only take a electrician couple of hours to wire it all up for you .