Pulsating brakes usually indicate warped drums on a trailer or rotors on disc brakes. If you are handy, I would jack up the trailer, set jack stand and remove each wheel and spin the drum and look for runout. Would probably be a good thing to take it to a reputable dealer and have all 4 drums removed and turned. As soon as the tech. gets the drum on a machine, they will be able to tell whether they can turn the drum or if it will have to be replaced.
Another possibility is that one or more wires on the brake magnets are loose and are activating and releasing. Inspect for loose connections first and if any are suspect, I would cut, solder and install shrink tubing over the connection.