You don't have to remove the tire/wheel. Some have been able to take the battery out by turning the wheel to give you access.
Thor's recommended method is to remove the passenger desk (flip it open and remove the rubber "cups" there are some screws. Unscrew the screws and the desk will lift out. The wood is perforated below that.
There these threads on that subject:
http://www.thorforums.com/forums/f8/...oval-3028.html
http://www.thorforums.com/forums/f8/...ise-10915.html
This one has pictures:
http://www.thorforums.com/forums/f4/...ment-5903.html
As far as the type: It's just a standard 12V car battery for an E-350 or E-450 chassis (I haven't replaced ours yet so I don't know the exact size--some have already on here--see above threads for more).
Thor Forums
