Ken: Thanks for your reply. I used to use a similar panel to charge my size 27 battery during the week, after cruising it on the weekends. I just laid the panel on the cockpit floor during the week, and put it in the car on the weekends. I also used a regulator similar to the one that you show.
As I said, my son wants to use this solar panel on top of his Bimini, so I will show him your photos. He also wants to use 2 batteries like you.
Last summer I bought one of the little solar panels from Harbor Freight. It's about 14 inches square. It was cheap, but it, of course, doesn't have anywhere near the output of the big panel. (I got the big panel for free at work after one of our customers sent it to us to examine. It wasn't perfect, one of the cells has a little chipped corner, but it was free, and it still had plenty of output). I now use the little panel to keep my battery charged, and it's OK, but not great. I do really like using the solar panel to keep the battery charged. I don't have to worry about a connection to the dock. Another thing is tha the batteries last years longer. I also keep them on floating chargers all winter. I tweak the resistors inside the floating chargers so that the batteries stay at 13.2 volts.
Thanks again, Aldo