There may two or three things you can check about.
The NEW DIGITAL NATL BROADCAST now operates on the low and high end UHF frequencies which really helps if your OTA BATWING antenna has the UHF add-on Dipoles. This gives you more gain for the UHF signals... Of course being higher in frequency you also have to be almost exactly centered on the transmitting signals from the local towns... Once you get tuned into one going through the scan-in process - see if you cant improve the signal by moving the batwing antenna a few degrees in either direction.
The WALL BOX the others was talking about looks like this photo. It usually has a cigarette lighter receptacle on it and a small push button switch to send power up to the BATWING anteena to engage the built-in preamp. You know it is working if you see a RED or GREEN light come on after you push the small switch. Your HDTV also needs to be using the type F connector on this wallbox insiead of the CABLE TV connector coming from the side of the trailer.
The BATWING should have an UHF set of dipoles mounted on it that looks like this
The one in the back is the standard BATWING antenna - the one in the front is the better UHF model version...
Some folks get great results by switching to a different UHF antenna called the JACK. This is made by KINGS CONTROLS and will operate from the same cable the BATWING and control wall mount in the trailer. Some of the new trailers are coming out with the JACK antenna installed which is not a crank-up version like the BATWING is. The Jack just rotates 360 degrees and doesn't protrude up beyond your roof mounted air conditioner install. You can also buy one that will snap right in place on your old OTA BATWING antenna locations and crank up and down just like the BATWING did.
When I am doing the initial scan mode using ANTENNA from the HDTV setup I will start the scan after pointing the antenna towards the local town transmitting the local Natl Broadcast channels. If I don't start seeing DIGITAL stations being counted during the first 15% of the scanning process i will stop the scan and move the antenna a few degrees one way or the other ans restart the scan process...
Like I mentioned you got be right on the transmission direction where with the old analog VHF signals you had some leeway in doing this... HDTV for the most part are perfect or nothing at at all- not like the old days where you would pick up a "SNOWY" picture and could move the antenna to peak it up. They do make some field strength meters you can find the signals and peak on that before starting the TV scan. I haven't had to use one of those yet.
Here on the East Coast I get excellent results using the OTA BATWING antenna with the UHF dipoles. We usually get 6-36 full HDTV (full screen) National Broadcast CBS-NBC-ABC-FOX-PBS transmissions just about everywhere we go. Haven't been beyond OKLA and TEXAS with our OFF-ROAD POPUP out west but with the towns further apart it probable is harder to do at many locations. Reception got so good for us we stopped bringing along the SAT TV equipment since we would rather watch the local BROADCAST stations anyway. If there is something we really want to watch on CABLE TV when out in the woods we just log into CNN-TNT-etc using the Verizon MIFI connections on the computer. This does eat up your dataplan big time but there are somethings (like movies) you really want to watch sometimes.
Hope this is helpful for you... ALSO if you are using the DIGITAL TV conversion box - get rid of that and go pickup a HDTV ready TV. We use the 22-inch HDTV made by VIZIO and it works great for us out in the woods. Even the squirrels and deer like to sit around the patio with us watching NCIS way back in the woods... I also love the 24 HR weather broadcasts on Natl TV. Being in a POPUP makes you keep an eye to heavens all the time.. Sometimes we get a BEAR at the table watching HDTV with us...
All photos from google images
This is the way I do the HDTV setups when camping off the power grids - I'm sure others do it differently - Works great for us...