Unified Tow Brake by US Gear. Been using it since 2005, three different motorhomes, 5 different cars (umm, maybe 6). Proportional braking. Never a problem, easy to hook up - tow bar, safety cables, breakaway cable, and the one plug for lights and the brakes. In all the 8+ years ran the battery down on one HHR and that was 100% entirely my fault.
It's worth looking into.