I bought a "window" adapter initially (they break easily) that was a flat rubber ribbon with a shielded wire in it so I could close the window and screen. http://www.summitsource.com/directv-...x8-p-6692.html
When it broke, I just routed the wire through the small rear window on the camper and used a piece duct tape to keep the bugs out.
If you get a longer extension you could route the wire through the gaps in a slide seal.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW