If you are looking for a supplemental brake system...

If you are looking for a supplemental brake system for a towed vehicle behind a motorhome, SMI Manufacturing has the best products on the market and their customer service is 1st class.

I had one of their early systems that you had to take in and out of the towed vehicle for 16 years. We never had a problem with it and it worked great for all those years. When we bought our new diesel motorhome with airbrakes, we had them install an Air Force One system. The system works proportionately so if you softly apply the brakes in the motorhome, the brakes are applied softly in the towed vehicle. If you apply the brakes harder in the motorhome, the brakes are applied harder in the towed vehicle. Another key feature is that it keeps the vacuum in the towed vehicle power brake system active so your power / anti-lock brakes work in your towed vehicle which then requires much less pressure on the towed vehicle brake system (and prevents you from locking up your towed vehicle brakes and potentially flat spotting your tires).

I can't say enough good about the company, the employees or the products, they are all 1st class. Next time I'm in the market for a supplemental brake system I won't hesitate to go back to SMI Manufacturing!