vac brakes.
you only need to run a 3/8th hose for vac supply, vac actuators are larger but you set up for vac off spring on and just use a tied in on a T piece with a QD down the back to hook up to the brake tank then plumb in as per electric over air.
If you're game enough you can set up so that it uses a blanced diaphragm and then tap both sides of your booster to make the trailer brakes come on at the same time and pressure as your normal brakes.

