Mondeo Les

I'm fitting a blanking plate in my replacement Mk3 Mondeo. The plate I fitted on my old Mondeo was great but after 230,000miles the rest of the car had had enough.

Anyway, the plate I bought came with a non metal

gasket. Question is this; why one gasket and which side of the plate should it go? (I can't remeber from the last time I did it. I had that Mondeo 15 years!)

Thanks.