A great many bike racks explicitly state that they are not for use on an RV or a car/trailer being towed by an RV. It seems the movement is different than when behind a driven car and most car racks are not strong enough to handle it.
The trailer/rv online seller eTrailer.com lists a number of bike racks for sale and they add a rating to each one showing if it's RV approved, Trailer approved, Flat-Tow Car approved.
I bought one to use behind my Toad (flat towed car behind my motorhome) it was NOT approved for that. I figured how could it be a problem? Well, I found out - it didn't crash and burn but it also didn't work well. The bike's hold down hooks got loose as I drove. I made it work by tightening everything back up at every gas or lunch stop. When I use the rack on my car when not on an RV trip I don't have any issues with things not holding. So, I guess it really is different back there.
Here's the rating for the
Thule EasyFold XT Bike Rack for 2 Electric Bikes
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