I may have a solution for you, but you won't be able to add panels to the Go Power Portable Solar Panel with Digital Solar Controller - 130 Watt Solar Panel # 34282730 because of the limitations of the charge controller. However, you could add a roof mounted solar panel with its' own controller like the Go Power Solar Flex Charging System with Digital Solar Controller - 110 Watt Solar Panel # 34272630 and expand your charging ability.
Unfortunately there's not a way to split the controller... view full answer...