I would recommend that you watch 2 RV forums. RVForums.com is a recent addition and is becoming quite popular due to its friendly members. Another is iRV2.com. More members and has been around a long time.
The first question is what are you towing with? If it has air brakes, then you can tap into the air brakes to activate the towed vehicle’s brakes. Air Force One.
If you don’t have air brakes, you must pick from a whole other technology. I chose RVIBrake. Compact, light, easy to setup, progressive and adjustable.
A towed car is often referred as a Toad. Searching for Toad Supplemental brakes should get you some options.