It's less the expansion/contraction differences between body plastic and metal than it is the difficulty in working a flat panel. A flat panel like a hood or roof has little strength so sanding & feathering a small spot is more difficult. I personally was never a fan of putting plastic on large areas but that seems to be accepted practice these days. If the prep is good, quality products used and thickness kept to less than 1/4" you'll probably be OK with the skim coat.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.