[dsraven]

if you have time you could also check the marine sites as a lot of boats have a heater under the seat. not ac though if you need that. school busses, work vehicles, industrial stuff, semi truck sleeper heater, etc. lots of options you just gotta find one that fits. a lot of guys have removed the glove box to accomodate the heater and ac unit. if you just want a heater you could look for a really common heater core unit that would fit your heater area chosen and then make a box around that and put a fan on one side with outlets on the other. its what I did with my boat because they don't make the size of core I needed.
just some ideas to think about. a local rad repaier shop may have some ideas too.