That amplifier is pretty lower power compared to most subwoofer amplifiers out there.
It looks like it'll draw 300 watts RMS (always look at RMS, peak values are useless), which will be about 20 amps. If you use an 8-gauge wiring kit you should be fine. Ideally a 4-gauge would be best. See below. I've not installed a sub on a 124 yet but the 201 and 126 were easy as cake.
Mercedes has a grommet right behind the battery area and you can use that to feed the power line to the trunk. You're "supposed" to feed signal RCA lines down the opposite side of the vehicle as power however I've never had any noise issues. So my power, remote turn-on and signal all went down the passenger side.
Take off the door sill, B pillar, and remove the bottom of the back seat. Run the three cables against the wall and then up underneath the backseat and finally into the trunk. Find a ground in there somewhere and you're set to go.
With only 300-watts to work with I think he actually might be going for better bass response rather than BOOM BOOM BOOM.
I have 1000-watts in my 190, but its only BOOM BOOM BOOM when I make it so. Also my trunk is covered in sound deadening as well. I also have two JBL amps running Boston Acoustics all around.
With only a 300-watt load I think the factory alternator would be OK with that. Looks like its a 70-amp unit. The subwoofer wont be running at 300-watts continuously so I dont think it'll be a problem.
