[Motor31]

The advantage to two 12 volt batteries is this. In the event that one fails you can simply cut it out of the circuit and you still have another 12 volt battery you can use. Having said that, the 6 volt batteries are heavier and you can generally get more amp hours from a pair of them than a pair of 12 volt batteries.

This is all predicated on what you plan to do with your rig. If you plan to stay at a park almost all the time (like we do) and dry camp a minimal time I'd go with two 12 volt batteries since it's generally a bit cheaper and they are easier to find (wally world etc.) If you plan on dry camping a good part of the time and will exercise the battery bank, possibly charging with solar or wind go with a 4 battery bank of 6 volt batteries. Trojan golf cart batteries are highly recommended but very very heavy and will require modification to the rig to hold them all.

Either way make sure you maintain the batteries, keeping terminals clean and water topped up about every 3 months or so. They should last 3 to 5 years that way minimum.