Check the websites for the e-bike racks as these racks will handle 120 lbs with ease. The Hollywood, Thule, Yakima, Swagman, and 1up manufacturers will specify if the racks need a 1-1/4 or 2 inch hitch receiver or can be mounted on a bumper.
Easiest to mount the rack on the tow vehicle and not off the rear of the trailer. There are dual hitch receiver adapters so the tow vehicle can be attached to the trailer and also have a place to mount a bike rack that requires a hitch mount.