Decide whether you are going to put holes in your roof or not. I decided not. My Winnie Class C has two windows on each side in the upper berth. I'm building a panel to replace the screen on the inside of the glass. I'll slide the window open, seal the panel in place, and mount all of my antennas on that panel. It will be an aluminum panel, but I'll bolt a piece of angle iron on it for my mag mount antennas (like the gps and cell phone). I'll have a CB whip mounted further out off the panel (due to the power radiated), but it will have a "swivel" mount, so I don't have to worry about Sallyberetta taking the corners too tight and scraping it off. :evil:
I'll mount "bulkhead" connectors (thru-panel) along the bottom of the panel. All of the cables will have connectors for easy disconnect on the inside or the outside. Everything will be sealed against water infiltration.
That sounds like a pretty good plan for multiple antennas. The only problem I see is 'ground plane'.
Many vertical antennas prefer to have a 'ground plane' beneath them. If you are mounting on a metal vehicle, that will do it. However a fiberglass unit will probably not provide such a factor, and the performance will likely be significantly reduced.
Some antennas claim to not require a ground plane. Some have some elements sticking out from the base to provide this and some have no obvious differences. I have no idea if or how well any of these work.
If it were me, I might be tempted to mount a metal sheet on my roof, and then mount the antennas to (mag mount) or through (hole in roof) that. Another option might be one of those trucker antenna systems which mount to the mirrors.
On my pickup, I mount a 2M ham antenna on the left fender sort of like the factory AM/FM antenna on the right fender. Don't know how this would work for a CB antenna. Also, they (at least used to) have AM/FM/CB antennas to replace the factory antenna. I doubt this would work very well since the best antennas are tuned to the operating frequency. The also have 'through the glass' antennas. Never tried one of these for CB, but the cellular phone ones I've tried pretty much suck (better than nothing, but not as good as direct wired).
The 'ground plane' on a MH will be the frame of the walls, probably. However, for all practical purposes, CB will work short distances from MH to MH with a wet noodle hanging out the window. Any other use for CB is probably wishful thinking, because you have to squelch all the profanity out anyway! :blush:
I don't know if this would work but it seams reasonable the ground plane doesn't care what end of the coax it is connected to.
Like Texas Clodhopper said the metal frame would be the ground plane.
You might try attaching a bare end of a wire (via a hose clamp) to the outside of the (PL259)connector of the coax. The barrel part, you screw the coax onto the radio with. Then ground the other end of that wire to a good ground. Do not transmit without the antenna and coax attached to the radio. Checking and setting the SWR to the lowest setting will tell you if it worked. If you can't set it didn't work. Transmitting just long enough to set the SWR shouldn't hurt your radio.
When you check and set your SWR, replace the stainless steal antenna whip with a braising rod the same size. That way you can cut the braising rod to improve the SWR. If it works and you get the SWR where you want it either just use the braising rod or cut the whip to the same lenght. If it doesn't improve you are only out your time and the cost of the rod, and you haven't altered the original whip of the antenna.
My guess is though it will work but really 2 meter ham is the way to go.
I don't get on 2-meters very much any more here since the CB'rs started getting their ham licenses. I controlled the local repeater for our club, but the CB'rs all got together and attempted to vote themselves into the club so they could control the repeater. Only problem was that that isn't how the system works! All they succeeded in doing is destroying the financial support behind the repeater, so I had to take it off the tower. No more repeater! Wasn't that smart of them? :dead: