New body panels

[Guyz55]

I am restoring my 55 2nd series short bed ....at the suggestion of the body shop doing the work , I have ordered new body panels like the front and rear fenders doors hood , because there was rust and the body guy said the project would come out better with new panels ...what needs to be done to these panels once they get to the body shop ....I have seen on car shows where they apply a skim coat of body filler ..Is that necessary ?

Thanx