From the tintdude.com
Concerns when tinting the new 2004 5 series
The door panels looks really tricky but I think I figured it out. Also the rear window looks pretty easy to tint but I know it would be similar to the newer 7 series with the electronics in the trunk. Sure enough I pulled back the panel and saw a bunch of electronics on the driver's side trunk.
My guess is to stuff a big towel there to collect any solution that drips down there but should actually keep a towel there for at least 2 days because there will be excess water that is still trapped on the rear deck lid and might not drip down unless you are making a turn.
From what I gather, the rear door panels are held together by 2 screws and clips. Pop off all the clips around the door after removing the screws and you are suppose to be able to lift the door panel right up. After you take the panel off, you need to remove this plastic clip off the door panel by depressing the metal tab. Stick that plastic clip back onto the door and when you are ready to reinstall the door panel, just slip the top on the door panel ledge and push the panel right back onto the door. Everything will lock back in and click together.
Do not try to remove the wooden trim like the older models because they do not come off. If the car comes with the factory screen, you will need to get a hook tool to stick into the top corner and lift the metal tab up a little in order to pull that screen off between the rollup and the quarter glass.
I hope I didn't miss anything. It is always a challenge to work on a new car and with cars that costs around $60K and owners that are very meticulous, I hope this info helps everyone out so they don't cause any damage while their car is being tinted. Good luck and pm me if you need further assistance. original link