Drywall Under Tongue and Groove?
You should be careful in your choice of wall paneling material and its preparation. Not all T&amp;G planks are suitable for walls period, and fewer still are suitable for bathrooms. Ensure your planks are sealed on all sides to minimize risk of warping.

For more flexibility, install a standard drywall wall surface. Then you can attach decorative paneling over that without compromising critical functions of the wall.