Ended up fixing it to the back of the centre console. You can reach the knobs to adjust stuff (although you can't see it without looking over your shoulder) and the mic falls nicely to hand on the centre console. Doesn't interfere with the arm rest being open either which is nice.
My CB is kept in the kangaroo pouch behind my seat. It's one of those GE emergency 40 channel units in its own case that plugs into the cigarette lighter and has a magnetic antennae. It works pretty well.