So - does anyone know of an omni directional horizontally polarized
wide band antenna?


Had something like that on the roof of my RV. A Wineguard Roadstar
2000 omnidirectional antenna ought to be just what you're looking for.
Paint it black, if you want even more stealth.

such as at: http://www.amazon.com/Canon-Winegard-Roadstar-2000-
Antenna/dp/B000R2YB0G

Ed