I too was frustrated by the reception with my antenna. Our local favorite spot, which is only about 15 miles from our house (State Park), should be able to pick up close to what we get a home. Over the years, with different RV's, we've had varying success with the built-in antennas.
With our current RV, I was looking to upgrade from the included Winegard Sensar II to something better. Saw the 'wingman' add on for the Sensar antenna, and also saw an ad for the JACK antenna. I ended up buying the JACK, which directly replaces the standard Winegard Antenna and really didn't find any appreciable improvement over the standard one. While I was at it, I checked all the connections to ensure everything was good and in place - again nothing found wrong, just not a good antenna. In my Cougar 291RLS, the antenna amp is behind the wall plate for the TV in the bedroom.
The best luck I had was making my own antenna, and plugging it into the external antenna connection, and using a different amplifier. At the same location, I now get 12 good channels, and 4 weak ones, versus 2 weak channels with the built in. Personally, you'd think the EE's would be able to make a good TV antenna for $50, when you can make your own, and better for about $3 in scrap wire and a coax connector. If I just hang it on the side of the RV, I have to move it to get different channels, but if I hang it from the existing antenna mast, I get the 16 channels without moving it around.