I mounted the CB antenna in the center, just behind the windshield. On my 100" WB, that puts the 11m antenna about even front to back, with the hood and the roof, and as much side to side groundplane as I can manage.
I mounted the hamstick on the LF corner of the roof - I wanted it high, but also needed to be able to lay it down. This location lets me lay the antenna down alongside the spare tire, and it's also handy for me to reach out the window and fold it over.
On the opposite (passenger) side, I put a 2m antenna, arranged so it has a full 19" of metal all around it.
Later, I put a second VHF antenna on the driver's rear of the roof, again, 19" from the edges, but also as far from the first as I could manage.
I used the second (rear) antenna for a 25w APRS station, while the front antenna is for the 65w VHF voice station.
I found that I had to bump the squelch up on the CB just a bit above "normal" - if I adjusted it just to where the background noise goes away, when I would key the VHF radio I would get some noise out of the CB. Another smidge of squelch cured it.
Operating 100w HF, however, did some unpleasant things to the CB.