tongue mounted bike racks are much more expensive than other choices.
can't you use your tow vehicle for the bikes? that's the best option.
truck bed or a roof rack system from Yakima or Thule. some use a front hitch bike rack.
you don't list your trailer so don't know if it's an ultralight or not. if it's an ultralight, rear mounted bike racks are not recommended, unless a receiver is welded AND braced to the frame and bumper. but this mod, as Herk's pic showed, will void the frame's warranty on an ultralight.
my bikes are not cheap and i choose to put them where i can see them, not on the back of a trailer that blocks my vision.
as others have said, this subject has been beat to death over and over.
by doing a search on any RV forum, you'll find suggestions, pics and enough reading for months.
and Zoe the Wonder Dog(R.I.P.)
'07 Roo 23SS pushing an '07 Chevy Avalanche
Equalizer WDH and Prodigy BC