Lots of votes for OSB. Just my opinion but when I built my wood shop in 2004, I went with drywall.its dirty now but its been up there a few years now and holding well. I didnt tape anything or paint anything I could make notes on it while talking with customers on the phone. My neighbor had a wood shop and he used OSB but his shop was an old pole building. It looked good but I liked the finished look of the drywall. I dont like to drive nails into walls and prefer shelving that I can screw right to the studs. I use whats called TUFF TRACK and can be bought at big box stores and is easy to install and its adjustable with out putting a lot of holes in the structure. Had I built a pole barn I may have went with the OSB and the possibility of covering it with drywall later! I like the dry wall but its whatever is best for your eyes and as long as it shelters the RV as planned.