I actually mounted the rack yesterday (Saturday), but once that was done I started on the antennas. I originally had plans to make fold over mounts for them so that I could just drop them down, but I am short on time with the Moab trip coming up next weekend so I decided to just make fixed mounts. I stood around in my workroom for a while Friday night after getting the radios installed, trying to figure out just how I was going to mount the antennas.
Since I am a bit of a packrat when it comes to potentially useful things (I save every nut, bolt, screw, and washer I have spare, as well as wire, electrical/electronic bits, and any brackets or whatnot, and numerous other things) which was very useful this time as I just so happened to have two bits of aluminum angle that came from a printer type thing my brother in law gave me that I tore down for parts. Not only did these two angles happen to be just the right size, but they also just so happened to each have a hole on one side that was a perfect fit for the CB antenna mount as well as my NMO mount for my 2M radio to give clearance to the center pin. And to top off the fortuitousness they were already anodized black!
All I had to do was drill holes for bolts to use as clamps in each bracket, and for the bracket I was going to use for the NMO, two more holes to bolt the NMO mount on. I also had some aluminum U channel (from that same printer) that was perfect to use for the clamps.
Here is the start of them, this bracket is about 5/16" thick I think, and the other is 1/4" thick. I used the thicker one for the CB antenna since it'd put more strain on the bracket than my much thinner and lighter 2M 5/8's wavelength antenna would. Though it probably still would have been fine.
Here you can see the hole I was talking about, plus each bracket had a tapped hole for a 10-32 bolt that I would use later for bonding.
I used some rubber packing I got from Lowes in their plumbing section to protect the paint and give it good hold.