Originally Posted by Siamese
I would typically suggest a bank of two 6v golf cart batteries and a 12v starting battery for emergencies, but for the needs you stated, a conventional lead acid deep cycle battery will serve you well. Keep some distilled water on board and top off the battery regularly.
Agreed. The advantages to the 6V GC batteries are high AH rating for their size and cost, full deep-cycle capability, a smaller footprint that gives you some mounting flexibility, and an easier job installing and removing them. Sam's club also sells GC batteries, as does Batteries Plus.
I agree you would do fine with a conventional 12V battery, but at least spec out a pair of GC batteries, you may find that works better for you.