Since battery gasses are flammable/explosive, I would NOT vent your batteries along with the refrigerator. Also, it's a waste of time when your area only sees 30f. The batteries won't freeze as long as you keep them charged.
My opinion is that it is always worth while to go with MPPT. And go larger than you think you need.
I also use the EPever Tracer. I use the AN, which is negative ground. The A positive ground works fine in an RV, but why not stick with the AN, which is newer anyway.
I use this one, which I think is a good package price. They make some smaller ones if you want to look them up.
EPever Tracer AN, 40A
