
You will quickly learn there is a lot of debate about the need for a supplemental brake system. As far as I know, there is no national standard or requirement. There are no independent comparison tests of the various supplemental brake designs, and the states have differing laws. Some states have a "performance standard" for braking, but I'm not aware of anyone that has ever had their vehicle combination stopping performance tested. I understand Canada requires supplemental brakes, but when we visited they neither asked us about, or inspected our Jeep to see if we indeed had supplemental brakes. Various web sites offer state by state lists of towing laws, but these are usually run by somebody that has skin in the game and the information presented is often inaccurate when compared to the actual state laws.
Here are a couple articles I think you may find useful. I especially hope you will read the article about the physics of towing a vehicle...
Towing a Vehicle includes information and photos concerning the necessary hardware to hook up any vehicle for towing.
The Physics of Towed Vehicles answers the question "would you rather be hit in the face by a baseball thrown at you by a 5 year old kid, or an MLB pitcher? It's the same ball right?" It really is all about mass, speed and momentum.