I'll bet most that are having an issue have solid wall TTers with rubber roofs. Antennas need metal ground plane to work correctly. Had the same issue with two way radios on boats 15-20 years ago. Had to use a 12" x 12" metal area below antenna to allow them to work. Discovered metal duct tape worked great since surface rarely was flat, it was easy to cut to shape, and it was stuck to gel coated fiberglass. This however would NOT be an option for rubber roofed trailers. The adapter to connect radio to the TV antenna is an excellent solution.
16 Silverado 3500 HD 6.6 Duramax 4X4
(Still looking for newer FR 5er)
Ultimate Aluminum 5th Wheel Hitch, TST tire monitors
Retired February 3, 2014, Bob & Cindy