Genarally, most vehicles require trailers over 2,000lbs to have their own brakes. As well, most states require brakes on trailers over 3,000lbs. While a towed vehicle may not be thought of as a trailer, it meets the technical requrements, as well as the "spirit" of most state laws.
I fear that many motorhome owners are far exceeding their brake capacity of their rigs by flat towing their vehicles with no brakes. Of course, this is not usually an issue with dolly towing as you can easily outfit them with surge brakes, but outfitting a dinghy-towed vehicle with brakes is perhaps the most difficult part of the installation.
When selecting a braking system, you have two choices; a permanently installed system or portable system. The permanently installed systems can be further classified into several subtypes:
Portable systems are those systems that are contained in a box that sits on the floorboard of the vehicle and are actuated by an accellerometer circuit. Whenever the circuit detects the vehicle slowing down, it applies the brakes. Such systems offer either air powered such as the RVIBrake or Brake Buddy systems, or electric actuator, such as the Blue Ox Patriot system.
No matter the system you choose, there are advantages and disadvantages to each, so your application will dictate which system you go with.
Proportional vs. non-proportional systems. A proportional system is one in which the degree of braking of the towed vehicle braking system follows the braking of the RV. In other words, the towed vehicle brakes are applied "in proportion" to the RV's brakes.
This means if the RV brakes are applied lightly, the towed vehicle's brakes are also applied lightly. And in a similar fashion, if the RV goes into a panic stop, the towed vehicle will also brake accordingly.
Conversely, non-proportional systems have a braking adjustment setting wherin the brakes are depressed by a certain amount of force each time the vehicle brakes regardless of the situation. This braking system is highly dependant on it's initial adjustment, and can often result in the towed vehicle braking too much or not enough. This can cause excessive brake wear on the towed vehicle (if set too high) or the RV (if set too low).
Generally, the portable systems use proportional braking, as well as the vacuum systems used with diesel pushers and the surge type brakes. The permanently installed brake systems that trigger off the RV's tail lights are often not proportional. But exceptions exist for every type of system, so if porportional braking is your desire, make sure the system you are contemplating includes it.
A few braking systems even include wireless remote controllers in the RV's cab so that you can monitor the system. As well, some additional goodies are available with some systems, such as RVIbrake's optional towed vehicle tire pressure monitoring system.
RVIBrake2 Portable Brake System Video.
Portable Braking Systems.
Installed Braking Systems.