Thought about it, but for now I usually just run a 12v extension cord to my fridge and leave it at that. I did disconnect it a couple months ago as it's cold enough outside (and I had only water bottles in the fridge) that I disconnected it. I did try and start my truck yesterday after it's been sitting for over a month; did the suspencted rrrRrrrRRRrrrrrRRRrrrrrr and then fired up (1HDT with dual batteries but converted to 12v start).
I have contemplated just leaving my 50W solar panel on the roof rack. With the fridge not plugged in it should, I think, keep the batteries topped up. I'll try to remember and test that theory while I'm off for the holidays.
The panel is not large enough to keep things topped up while the fridge is running, that much I know. It will charge up during the day (sunshine dependant heavily at this latitude), and then the fridge light will be flashing in the morning.
Alternatively, I bought one of these
Noco genius smart chargers awhile back, It is supposed to be able to be used for "Storage" conditions and can be left plugged in.
I did plug that in the other day after the slow start. I'll keep checking on it and see whats going on.
edit: during the 12v starter conversion, the left side battery (when standing in front looking at the engine) is the dedicated accessory battery. There is a marine grade isolater that switches over and charges either battery depending on need.