Just a little tip to make your battery box a little easier to deal with, look into remote mounting a heavy duty plug thing to hook jumper leads into. Saves climbing into the back seat every time you have to jump start the car, also allows you to be able to jump start others. Will try to find you a pic of the plug in connectors I am talking about later.
Callum
EDIT: This link gives a good example even if for a different purpose.