Many trailers, and I would imagine at least some dollys, that don't "have brakes" DO have the mounting flanges on the axles that allow bolting a brake kit on, easy DIY job. If boss has done a brake job on a car or pickup, can do this. A good welder could of course add those flanges.
Dolly may also have a bolted on (vs welded) Coupler, which would be easy to replace with a hydraulic Actuator (master cylinder) to apply Hydraulic Brakes.
Or... Add Electric Brakes and install a Trailer Brake Controller in the RV. Rental dollys are Hydraulic Surge so no controller is needed. If I was going to dedicate a Dolly to one RV, I'd add Electric Brakes and a Controller.