You can search this sub forum for details on what some of us have done for solar upgrades. Many of us have also upgraded our batteries. Here is a link to my recent post on my solar upgrade.
You could also go over to the Sprinter-Forum to find info on many more solar upgrades on Sprinters. Solar in the 300-400 range changes the whole dynamic of using your Interstate.
Hope this helps,
- - Mike
2013 Lounge EXT on 2012 Sprinter