Got me some newer Mopar to drag behind the coach.

Sounds like you scored on your RV coming with the towing gear. No disagreement from me on the brakes!
Miata curb weight 2100 lbs, Xcursion weight almost 11k lbs., obviously can't tell it's back there. I'm guessing your Dart is a little over 3k lbs. and mountain driving would make brakes a no brainer.

Yes for sure. Dart is like 3k or less curb. Easier on the coach brakes. The fish weighs 3400/3500 with original BB, and the 10K enclosed trailer weighs? Looking to install a proportional controller on the trailer A frame for it. Easy to install and not have to put a control box under the dash of the coach. The Ram 3500 has a built in controller and has been awesome but installing one on the trailer allows me to lend it out for anyone with a truck stout enough to pull it regardless of a brake controller. The Coach is pre-wired for it but would really not like to put one in. That flat tow is self contained so that works right in to the plan.