Back bumper is not really a bumper. At best, it's "stinky slinky" storage and maybe a spare tire carrier.
Do yourself a favor and have a 2" receiver installed on the trailer frame. Then buy a reliable i.e. good bike rack designed to mount to the receiver. This will allow you to safely carry the bikes while towing plus move the rack to the truck if you need to take the bikes to a trail head or someplace other than the campground to ride.
2017 Cougar 279RKSWE
2007.5 Dodge Ram 2500 6.7 Cummins
Retirement Training Completed
Mr. Rodgers did not adequately prepare me
for the people in my neighborhood