You do get microwaves to fit in vehicles, certainly trucks, my brother is an ex long distance trucker. I know trucks have 24v electrics, but i am pretty sure he said to me once that the power points in the cab were 12v. He had a microwave, coffee machine, fridge, tv/dvd player!.
On a separate note, i have my pump controller wired directly to my van battery. It came with wires and instructions to do so, and was not difficult.