I've been towing a 2500 pound double jetski trailer for thousands
of miles, no issues. Sometimes the BMW doesn't have enough guts
to pull the trailer out of a steep ramp. But when I turn the AC off
it is enough of a help to do it.
I am getting a 4x4 Tundra for future towing and using BMW as backup.
I used aftermarket hitch, no BMW electrical interface. I did have some
bulb warning issues so I switched out the Trailer lights for LED's which
have very little current draw and it has worked fine. BMW can keep their
$200 part....................