I put a Draw-tite on my '99 ML-320 when I bought it in '98 and it has worked fine. I still recall drilling the holes in the frame for the reinforcing brackets as being a tough job.
You need a converter from the Euro 4-wire tow lights to the American 3-wire so you might as well put it in the knock-out panel under the compartment at the rear of the driver's side. That's where you access the loom anyway. I've been through a few converters and finally caught on that a good one can use that separate fused B+ wire to draw upon and switch as it monitors the voltages in the stop/turn/tail light wires.
On wiring, solder everything! Crimped connectors are just a problem down the road-especially where trailers are concerned.