Fred, My solar controller is mounted on the ceiling of the compartment just ahead of the drive axle, the large pass thru bay. AM Solar of Eugene Or, I think, did most of Beaver solar installs. My panel is a 100w panel, can't recall the size of the controller, but it won't handle additional panels. By the way, the rule of thumb for solar is 100 w of solar per battery in your battery bank. SO, 4xgc2 batteries = 400w solar. Solar is just an expensive battery charger, not a primary power source. For each 100w solar panel,You should expect about 5 amps of charge current for 5 hrs/day or 25 amp hours of charge to replace what you draw from your battery bank. More panels, more amp hours.