Thank you, Bernie! I have one of these side panel mounts on the way.

Since my coax has the PL259 connector I figure I'll need to chop that off and solder on some spade terminals to connect to the screws on the back of that mount.

When I do that, is it OK to shorten my 18' coax cable? I have about 4' more than I need and it'd be cleaner to shorten it rather than coil it up under the car. Also, since I'll be separating the shielding from the signal wire, I assume I'll want to keep the new leads as short as possible, right?