I did something almost the same here with my JENSEN Car radio install on my POPUP trailer. It has two hot wires and both were tied to 12VDC so when it gets turned off it looses all the setting etc... Then when I first hookup at the camp ground I have to go thru all of the setting etc...
I picked a panel ON-OFF switch from radio Shack when they was still around and installed in the ignition key wire. Then when we get to the camp ground I can turn on the whole radio with the switch on the radio and then use the new switch to turn on and off the radio like you would do in your car. With the main part of the radio still ON all the time it remembers the last settings.
Of course most of the setting have to changed anyway from one area to another but at least while you are at the one site you can turn the radio on and off and retain the last settings you had in.
Roy Ken