I build an insert for rap-around seating then mounted Yakama truck bed mounts on the front of it so we can carry two bike on the inside of our 13 ft boler.
That's pretty slick. I've been wrestling with attaching a receiver hitch to the bumper so I can use the same hitch-mount bike rack I do when I'm not pulling the trailer. It's worked insofar as the bikes haven't fallen off, but the bike rack, the bumper and the frame all flex so much that I keep breaking the welds. So I keep putting more angle iron, steel and bolts back there to reinforce it. If I ever get it totally solid, I'll post pix up -- if I'm not too embarrassed with my Frankenstein fabrication.