Hi Terry, I think this can help you: https://thediyplaybook.com/2016/07/shiplap.html
Hello Terry! I have manufactured wood ship lap on my bathroom ceiling! I painted it after I put it up using a brush for the grooves and a roller for the rest. It was already primed when I purchased it. It looks great and I have had no moisture problems. It is installed on the ceiling above the tub/shower. I see no reason why it can't go on the walls if you are worrying about bathroom moisture.
This is Linda. I think that is a great idea. Due to the manufacturing process it should all be uniform so you shouldn't have problems installing it. I also think it would better in a bathroom than wood due to the moisture. While you're doing it, how about taking pictures and posting it as a project for all of us to see? It's really easy to do that, just click on the +Post Project link at the top of the page on your computer and follow the directions. The system will "walk" you through it. Have fun with your project!