the only way to do what you want to do, is to have a receiver welded and braced to the frame.
but, this mod will void the frame's warranty if it's new.
remember, popups and other ultralight trailers, don't have beefy frames and putting bike racks on the rear, to the bumper or the frame, could cause failure because of the physics involved.
imagine a pipe attached to the bumper and then having your 150lb. kid stand on the bumper and grab the pipe and lean back, pulling it back and forth, over and over again.
that's what a load of bikes on a bike rack will do.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC