Best way to keep chassis battery charged over winter?

There is a device that will monitor the chassis and coach batteries. If it finds the coach battery is above 13 volts and the chassis battery falls below 12.6 (or so) then it will energize a wire going to the chassis to coach battery relay. This allows automatic chassis battery charging.

I would just use the battery tender, and might even remove the clips and hook it up all the time to 120 volts in the basement, with the wires extending to the battery with #14 wire and a 10 amp fuse at both ends.

Fred.