Typically want to draw power from the MH to keep the dinghy's battery charged...
In the case of Invisibrake - it handles charging the dingy battery for me - taking in the MH 12v and direct connection to dinghy battery (only thing connected to dinghy battery when towing - the rest behind a disconnect as Jeep recommends for my Wrangler.
I've seen others just run the MH hot aux (from 6 or 7 pin connector) to the dingy's battery (fused) to charge...
There are also after-market chargers available that make use of the MH as a charge source.
The brake system does need connectivity to the dinghy battery to work in a breakaway - but use the MH to supplement/charge along the way.
Not yet retired...
Florida (Michigan transplant)
2014 Hurricane 32A
2000 Infinity (previous)