:) we finally got approval to build rv garage and workshop on property contractor asked what I would like on walls. sheetrock or OSB he said he liked osb because I could nail to it. isnt osb sort...
I assume this is a detached structure, so fire resistance should not be an issue.
Mine is a garage sized shop, not a RV sized barn, but I used T1-11 8" OC exterior siding on the interior walls. I think it looks nicer than OSB or plain plywood. Water proof if you ever get any inside, and very durable. Since it is lapped at the joints, it is easy to remove a sheet to add utilities in the wall cavities. I like the wood tone color, but could be painted if that's your thing.