to be fair, every time I've done this, it's been outside/inside & very well ventilated, and the tank has usually been out of the vehicle... like Donovan has pointed out, if you're using electric anywhere around the tank, make sure you have a fire extinguisher handy... the place I've done this before has around 8 within 1500 square feet...I would highly recommend against this. I nearly burnt The Juggernaut to the ground and killed myself in the process doing this many years ago. One wrong move and your life can change in an instant.
Ask me how I know. On second thought, don’t. It’s not something I particularly care to relive.