Disconnect Jensen Dash Radio

If it is indeed connected to the chassis battery, there would be a fuse in the chassis fuse panel for the radio standby (and possibly some other things). It may even be labeled sensibly if you're really lucky. Note that this may well not be the main fuse for the radio, since the memory line is a different connection than the main power (and typically the main power is switched with the ignition).

Disconnecting the battery negative cable would be the simplest and surest approach, I think, and also eliminates any other parasitic drains.

Do check that the radio circuits are actually powered by the chassis battery. Mine is wired to the house battery, and some have a switch to select which battery is used.

If you can get to the back of the radio you should find a plug going into the radio. Should be able to unplug that and then plug it in next year.

I'd probably disconnect one battery cable.