your trailer has an ultralight frame and if it's a newer one, there should be a sticker on the bumper telling you not to do something like this.
a number of members have pics of the sticker.
the cheap and flimsy welds on the bumper will not tolerate the load of bouncing bikes on it.
the only way to safely do this, is to have a 2" receiver welded AND braced to the FRAME.
but this mod will void the frame's manufacturer's warranty, unless your Rockwood is an older model and the frame warranty has already expired.
an easy search here will give you weeks of reading on your question, since it's asked all the time.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC