Dont run the baffles most speakers are designed to run in an infinite baffle type of set-up, choking em with the baffles will most likely kill the midbass response, though if you just want to have a lil sound for the passengers you could probably do it, it wont be optimum, but you wont need optimum for a lil rear fill, plus the music reflecting off the back glass already amplifies it.
Also I still have a pair of by 9's in the rear deck, and the pressure doesnt effect them, though that is probably since I am firing the subs into the cab sealed off from the trunk........