GC2 batteries: help me pick power supply for maintenance

Are you powering controller from some 12V supply? Because if you are not, the issue with "power supply for maintenance" remains unresolved.
160W panel will work as such maintainer, but not always. Depends on location, time of the year and how badly you've depleted the batteries before putting it into "maintenance mode" between the trips. You can't rely on being always able to equalize on solar whenever you feel like. Not with this ratio of solar W to bank AH.