If you use a constant 12v source you would have to manually turn off the radio. I've gone both routes on the CB - constant and switched power - and found that I vastly prefer the constant power. It's amazing how many times you would like to have your CB working when your truck is shut off, like when the group behind you is stopped a half mile back for a repair. The CB won't draw much power and I've left it on overnight with no ill effects.
You can get that 12v power a few different places - 12v outlets (tapping into the wires behind the dash panel), direct to the battery, Add-A-Fuse to the fuse box, Blue Sea Fuse block. It might be a good time to plan for the future and set up a central system for adding 12v power for multiple items: cb, lights, aftermarket lockers, sirens, ejection seats, etc.
http://www.amazon.com/Blue-Sea-Systems-Circuit-Ground/dp/B000THQ0CQ/ref=pd_sbs_auto_2
I have this mounted on the firewall with one heavier gauge wire to the battery, and one to a ground, and then the power/ground wires for each accessory run to this block. It's greatly cleaned up my wiring and now I don't have a bunch of wires going to the battery.
And, since you have an 06 you likely have the lousy battery connectors too. It's good to upgrade them and if doing an install like this a connector like this one is a good way to go:
http://www.amazon.com/gp/product/B000KIV23Q/ref=wms_ohs_product?ie=UTF8&psc=1 (There are lots of options and opinions on these connectors; this is the one I went with). This allows you to easily add accessory wires to the terminal without having to use the tightening screw like is required on the 06 and early 07 battery terminals.
