:) 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...
Another suggestion would be plywood painted with fire proof paint, although the paint is $$. FYI half inch drywall has a 30min fire rating and 5/8th. has a 45 min. rating.