C/B Antenna
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).