I, and several others in our camping group, have been using Costco batteries for over 10 years. I replaced the last set after 7 years of use only because I thought it was time.
When you do pull the trigger, take a look at this battery box
*LINK* IT nicely holds four 6v batteries in one container. They also have other size combinations. You will have to add a top vent, but that is pretty simple with a couple of PVC pipe connectors.