I've got an oven big enough here at work that could easily accomodate 3 large (think Chevy B-body) cars. Unfortunately we aren't in the powdercoating business... at least during weekdays.
That being said I would much rather e-coat a car than powdercoat. E-coating gets EVERYWHERE because it's dipped.
I'd also be worried about possible warping the body because of the 400F or so cure temps...