1.   Before attempting to mount the plywood, locate all the ceiling joists and the wall studs.

2.   Fasten the metal channels to the wall studs with wallboard screws.

3.   If you have two shorter pieces that must be spliced, plan for the joint to fall over a wall stud.

4.   If the towel bar is the right length you may be able to mount one, or both of the escutcheons directly to the wall studs behind the drywall.

5.   In the closet, find the center of each wall stud and also the ceiling joists.

6.   In that method the wall studs extend from the foundation to the roof.

7.   Inspect the wall studs for protruding nails.

8.   It has cathedral ceilings, and I can see the outline of the trusses on the ceiling and the wall studs on the walls.

9.   Most window frames are held in place with finishing nails that go through the inner and outer casings into the wall studs.

10.   Now, he can nail through the cleat into the wall stud, and no one will be the wiser.