go with an insulated bottle. at least one of these is bound to fit.
http://www.rei.com/search?cat=492768...AWater+Bottles
I have the 24oz novara, never tried to put it in the door. Its actually an insulated bike water bottle, and BPA free.
oh yeah.. and for the health freaks that are crazed about BPA.... metal containers aren't any better... they have ill effects as well... BPA free plastic is a much better option than metal... A metal with a coating like latex or some sort of rubber is a different story however.