I am getting ready to purchase one. One I am looking at has covered sides and divider from the cabin. I was thinking to build shelves with 2 x 4 framing and plywood.
The 2x4 takes up a lot more space than a 1x, just keep that in mind. I do have other parts to my build if you check out my Sprinter van playlist here, ru-vid.com/group/PL3SQwu9g6nXRp7-g8zuTfSluuIfUxf-bY I explain why I built my van out in the other videos. Good luck with the build out!