My motorhome has Styrofoam ceiling panels with the foam backed vinyl sagging and falling off.

My motorhome has Styrofoam ceiling panels with the foam backed vinyl sagging and falling off. I plan on installing a new ceiling over the styrofoam made of thin luan plywood with headliner material glued to it. Does the wood need to be sealed prior to applying the adhesive?

The luan plywood surface is already very smooth, and we have used it in many different applications in our local shop. You will not need to do anything to it before applying the headliner material to it. With this type of smooth surface, you should get a very nice looking job in your motorhome.