Here is neat little diagram showing the Antenna Panel and its operations...
Google image...
Sometime if you have LED interior lights in the trailer they may interfere with the HDTV signals. This usually happens when you are using the OTA Batwing antenna but could fuss up the cable tv port I guess as well...
Try turning off any LED lights that may be on...
Then you always ask yourself what else have I done recently around the RG cables.
Also it appears some of the Camp Grounds are now going with the digital HDTV signal being distributed around the camp ground. Are you using a Digital HDTV set... Guess this isn't a problem as you did state it works fine bypassing the outside CABLE TV PORT.
Does it do anything different by plugging in either of the two TV ports on your trailer. My has one labeled CABLE and the other labeled SAT. In my case both work the same using cable TV from the camp ground.
Found this photo in a JAYCO discussion... Have no idea what the jumper plate is for...
Heck if it all works good bypassing the external CABLE connection just run a RG cable down to the storage area and use that cable to plug into the camp ground TV connection... I have run a RG cable down this way for hooking upp a TV set under the awning. Closing the storage door on the Rg cable doesn't hurt mine at all...
Let us know what you eventually find out...
Roy Ken