We tried it and it didn’t work out too well.
The manufacturer doesn’t recommend adding a bike rack to the 4” square bumper on our Retro trailer. But we decided to chance it.
I added a CURT 19100 RV Bumper Hitch to the trailer’s bumper, slid our Yakima bike rack into it, and added two full size bikes.
We did fine on a 3,687 mile trip from Chicago to the Badlands and back. We didn’t do so fine on our second big trip to Arizona. About 900 miles into the trip, in Dallas, TX we stopped for gas, and I did a walk around of the car and trailer to see if everything was OK. It wasn’t.
I found the bumper torn at the mounts to the trailer frame and our bikes and spare tire leaning toward the pavement. (These photos recreated it in our driveway when we got home.)
Luckily nothing fell off. We were able to absorb the bikes, spare tires and racks into the trailer and car, and the trip proceeded.
Back home, we had the bumper replaced by our Riverside RV dealer and things are back to normal with the trailer.