I saw this low profile,
omnidirectional antenna from Radio Shack at a CG we were staying at. The gut swore by it for his digital signals, and analog.
The one I saw was mounted on a pole and guyed, but I'll bet you can put it on a ladder rather uniquely.
Edited:
At present, the digital signals are occupying the UHF frequency band. As analog goes away they will most likely drop down into the VHF band and free up the UHF band. That's what the whole switch to Digital was about, wasn't it?
So, for the time being, the present antenna you have will work. Until it is known what frequency band the TV stations in your area will be broadcasting in (Yeah! Your area in an RV) choosing an antenna now may not work with digital stations in the future. Wait until after June 12, 2009, and then decide which antenna to buy. They are supposed to have the frequency allocations sorted out by then.
Here is some information from the
FCC. Also a search on "digital antenna" with or without the quotes will get you a lot of information.
Good luck.