Robert
Make sure you take a picture of the batteries before you take them out.
It sounds like you will be having fun designing and installing your system. I'm very envious of the real estate you have to work with, I can only fit two big panels up top. I am considering putting the big panel I used as a portable on a rack under the trailer for when we need the extra power.
4 big panels (or more) will require a big MPPT controller. Have you begun looking at them? For two 245w panels I will get a 45a controller that will give me some breathing room when they run at full power.