I've been down this thought train myself when I had camper vans & for the car on days out at the beach. A mate of mine has a cheap Chinese diesel one in his work van. He's in the trades and works away from home a lot, sleeps in his van. He swears by it, not sure
I'd trust the build quality.
However, it was cheap, works well and was pretty simple to fit. The better built Eberspacher, or Webasto units will cost around 1k all in, Proper do an LPG version, a bit cheaper... and get a CO alarm!
There's
this electric one, note the power consumption on battery, but could work with a split charged leisure battery for short spells.
I think you need to ask yourself if you are willing to drill a few holes in your car for a permanently fitted heater, or whether you want something you can chuck in the back when you go stalking, ie Genny & 240v heater