You have the off-peak heat in your house, why not tie into that for power to your garage heat and eliminate the need for another meter. I am on the straight electric heat without a backup and have my garage hooked up to the house heat meter, but see no reason why you could'nt tie garage into your off peak. I have neighbors doing it without any problems. It is very seldom that REC goes on off peak so I  doubt if you would need a backup heat source.

The off-peak rate is your cheapest source of power. You may want to look for a little larger heater in the garage.  I would guess that we are on the same rural electric.