Are you connecting the meter to the battery before fully disconnecting the cable from the battery? If not you are going to see a higher reading than the actual draw because all of the control units that are powered with the key off are coming back on before going into a "sleep " mode. By connecting the meter leads before you totally disconect the battery cable keeps the circuit complete. Also be sure you have the trunk light bulb removed or turned off during this test.
Mercedes Benz Master Tech