What I've read from the guys on the Olds list over the years is to put the new skins out in the sun for a while prior to install so they'll stretch a bit easier to install.
The second recommendation was using a dry cleaning bag over the foam, and then install the new skins over that as the material will slide a lot easier over the plastic than foam.
Good luck, and let us know how it goes. It's one of the things I have yet to try myself.
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