To the OP. There is the Ditch Light mounting option. I found this to be great for GMRS one side and a CB on the other (yeah, CB for when on "The 5."}
I'm running an 8 watt handheld to that ~ 3db GMRS tuned antenna ($11), low SWR and hitting the local repeaters.
Your bigger issue, when its all said and done will be the coax routing and how you go through the firewall, if going that route. I went full in with a clutch delete plate (drilled it out) with an inserted boot for both coax and several two-pair of extra future use wires.
As for the extra couple of feet of coax on that side, that is all shoved in a BALL of WIRE up under the dash right where the truck thieves will be trying to find my OBD plug...................... (gone).
