Don't use Stress Evaluation only. That adds no material.

The choice between Membrane only vs. Membrane and Bending will have very little effect on the results because almost all the effect of the coating is a membrane effect. Adding Bending will cause extra equations to be added so it will take a little longer to compute a value that will have a small effect if the thickness is very small compared with the solid material.

In either case, you get to define the thickness and material.