I have the D2 unit which is the smallest one. Had it installed at Espar of Michigan. Total cost installed was 1600 bucks.
I am in a Sprinter which is not insulated at all. (bad idea). I have a curtain which can block off the back which leaves me heating about 80 inches of space by 60 inches.
My first night in it was 3 below zero. It kept me barely warm. I know if I was insulated it would have worked well. Anything from the teens and up, and if I have the thermostat set too high, I wake up sweating.
I don't know how much diesel it uses, though I would guess it to be about one gallon on a very cold 12 hours or so. It runs off my vehicle fuel tank.
It is very small in size (about the size of one size thirteen shoe), It has one very small control mounted on my sidewall Three buttons...on, off, fan only. And it has a small rotary switch to set the temperature.
It is extremely easy to operate, and sounds like a muffled turbo when it is running.
Hope this info is helpful.