I had a 2013 BH390 and there was a plug prewired under the dash to the left of the steering column. Easy to wire. The plug had an empty half that I removed and inserted my brake controller wires into. I purchased a few of the correct size electrical spades to complete the plug. My new Phaeton is wired exactly the same way.
Well I'm interested in this topic because I was told by dealer reps and a rep from FR that I didn't need to worry about towing my 2500 lb. dual axle steel trailer with a 1500 lb. RZR behind our Berk 38A. Had a number of MH friends say the same thing. Of course I don't expect anyone here in this forum to admit to doing such a thing. But I've seen a lot of class C's pulling things behind them that I questioned. Especially the "trains."