In addition to the statute 16ACE27 quoted - there are weight limits that vary by state... and this is one law that the state you are towing in is what matters - not the state of vehicle registration.
One source:
https://www.readybrake.com/state-towing-laws.html
Couple of states as low as 1000lbs (NY and NC).
My choice - I wouldn't tow without the toad brakes regardless of weight requirements... Towing a $20-40K vehicle with an $80-100K motorhome - the cost of a brake system is peanuts... I never feel my Jeep when I am stopping - it takes care of itself very nicely. Not elongating the already long stopping distance of the RV.
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