Mr Wiz is getting set to do the "two-bank" routine.
Another thing about fridges is here camping from Jan to March, it is as cold out as it is in the fridge, so why pay money to keep stuff in the fridge inside the warm RV? Convenience costs money.
There you are paying to heat the place you are paying to keep cold. At the same time as that, the furnace is blowing heat to the outside air that would be nice to divert that heat for the batteries which are sitting outside at lower AH because of the cold! It is all stupid if you think about it, so don't think about it. :)
Fridge's propane option is useful when 120v power is limited, but once the existing fridge goes bust, cost of replacing that makes Mr Wiz's method look good as long as your rig can be adapted for enough batteries etc.