One, the Jeep has vacuum assisted power brakes like the majority of all cars today. Two, Jeep Brake Assist activates when it senses quick brake pedal depression and gives the brake more force than you are actually applying. Three, you have Antilock Brake System (ABS) which pumps the brake rapidly when you push the pedal really hard. One is stepping on the brake pedal quickly and the other is stepping on the brake pedal hard. This works when the key is on and controlled by the computer. So, while driving, you have these three parts of the brake system working.
When towing the Jeep, the key is off, the engine is not making vacuum, and the computer is not monitoring anything. If you were to use a toad brake system, like EvenBrake, you place a box on the floorbaord in front of the driver's seat, attach a rod to the brake pedal, and plug in the electrical cord into the cigarette lighter. As you stop the motorhome, the box senses the decelleration and applies pressure on the brake pedal. Since there is no vacuum assist with engine not running, it takes tremendous pressure to push the brake pedal hard enough to apply the brakes to stop the toad. If you have ever experienced stopping a power brake eqquiped car with no vacuum assist, you know what I mean.
Now enter SMI. They apply vacuum to the booster without the engine running, thereby giving you power brakes when towing. Now it takes a lot less pedal effort (8-10 lbs.)to stop the toad. This allows a more compact design of their system. Air Force One uses a small cylinder that is permanently attached to the brake pedal, under the dash, out of sight.
So, in reviewing, you have vacuum assist power brakes when towing. And, when driving, you have vacuum assisted power brakes, hydraulic brake assist, and antlock brakes.
I hope this helps.
Harry & Sheryl
2008 Camelot 40 PDQ