Unfortunately, most LP grills (medium/full size) that would mount to a bumper have their own regulators and TT gas lines are already regulated down. You would have to add a tap before the regulator and run lines for high pressure - which isn't recommended for trailers, because if you have a leak, you could go BOOM! If you want to pursue this, check with your local LP store, they may have a tech that might want side work on a weekend to help. Professional help would be recommended for this.
If your trailer has a LP line run for a grill, it is already regulated and you would need a grill that only has a portion valve for flame height and non regulated for pressure. Double regulators makes for a non working grill.
Also, you can do a web search for "tailgating" grills, "Bumper" grill, or "hitch" grills for what you are thinking of. They are already produce them.
Bob and sometimes - Nina - a Staffordshire Terrier/a SPOILED pit and her kitty Spaz
2006 Dodge SLT 2500 4x4 Cummins Quad Cab w/AT and 3.73
2007 Salem Sport LE 26FBSRV (TH) w/ my Victory Motorcycle in it or a EZ GO Shuttle cart.