You sound just like me. Mine is also in a storage yard and I bring the battery back home after the season and hook it up to a maintainer, otherwise its in the trailer for the summer. I have a 100w panel and a morningstar 30 amp controller and also a battery disconnect switch. It has performed flawlessly in the many years I have had this setup.
The battery is always on float charge when I check it and like you I do go to the trailer and have to open a slide or use lights.
I think I bought the panel from Solarblvd - which might be out of business but I saw some 100w panels at home depot from Grape solar that were cheap. 100W might be a little overkill for just keeping the batteries charged but they had a sale or something when I bought it and it wasnt much more than a smaller wattage panel.
