This is how I removed the rear bumper on my E320.
You are taking your own risk.
1. open the trunk
2. remove the spare tire
3. remove two side pockets - you will have to unhook few clips(where the CD changer is)
4. on the bumper side and two pocket sides of the truck, you will see few screws. Remove them
5. After removing all the screws, carefully slide out the whole bumper toward you
6. you are done.
***when you put the bumper back, be EXTREMELY CAREFUL not to put too much pressure on it. I made holes on my bumper because I didn't pay attention to the bracket that holds the bumper.
Again, I will not be responsible for any damage you may cause by following my direction.