The way the AGMs pay for themselves is in reduced engine hours for charging and reduced manhours for engine maintenance. So, you need to be charging your batteries every day AND have a large enough alternator to take advantage of the increased charge acceptance of the AGMs. If you're only cruising a few weeks a year, I doubt if you could make a case that the AGMs would be cost effective. As for Gels, only if you plan to use them on their side or upside down - leave them for the aerobatic aircraft.