When I bought the 5er I have now, I bought a Garmin RV760 GPS and the BC-20 backup camera with it. The 5er had the preinstalled Furrion camera mount below the center running light with power so I mounted it in that and put the transmitter just inside the back wall in the cabinets. You can probably find my install thread pretty easy.
Initially, I thought the signal was OK - a little jumpy at times. However, when I went to Florida last winter, it became a bit of a pain because, since my truck has automatic headlights (that also turn on the running lights and thus the camera) the GPS would switch to the camera view whenever the lights came on. This was usually near the end of the travel day, just when I was relying on the GPS route map to be up all the time to find the overnight destination. Normally, this wouldn't be a problem - just hit the GPS 'back' button to go back to the map, however since the signal was flakey, the screen would just flip back when the signal returned (there's no setting in the GPS to disable automatic camera switching).
When I got back, I ordered the extension cable, ran it down the back wall (on the inside), behind the sofa, through the hole in the floor that the freshwater fill goes through, zip tied it all along the propane pipe and remounted the transmitter right beside the front basement door. I picked up power from one of the side running lights and now have a beautiful signal.
Long story short, the Garmin can be made to work but depending on the length between the back of your trailer and the GPS you may need to get the extension and remount the transmitter toward the front of the trailer.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam