I have a CB antenna in the center of the roof on my Promaster van. Had it in 2 CB shops and the SWR is still above 2.5. It was 4.5, got it down by adding a 12" mast raising the coil 14" above the roof. I was told the roof is the absolute best spot for both transmitting and receiving. It does receive better with it raised up but transmitting is only slightly better. 10-15 big truck lengths in any direction is about it. I had a cobra ltd 29 on it. Checked out good no issues. Replaced it with a new Uniden 880 same results. Replaced the mics. Changed the new coax for new coax 18' only because thats what it takes from point A to B. Replaced the new wilson 2000 with a roadpro antenna with a 12" mast. That helped the most of anything I've done thus far. (Tried 6", 8", 10" mast not much difference.) The wilson on the 12" is also better. SOOO my question is is there anyway to shield the ground plane on the roof from the antenna base so I don't have to run 20" mast with a 4' whip with total height of almost 6' ? Maybe a disc of some type 12-14" around under the mount? Lost on this one. It's been like this from day one. With everything new. The coax has an external ground wire spliced into the ground shield on the coax and grounded to the vehicle as well as the radio, radio mount and roof base. So I'm really sure it's grounded really good. Anyone else running a roof mount on a van with no issues or the same issues?