Fiberglass is alive....It expands and contracts with temperature and humidity...The steel in the Corvette stays fairly rigid (ya think?) and the fiberglass moves all over the damn place...On a boat, the hull can change shape by an unbelievable amount.
We used to let the bow winches and transom tie downs loose on our boats when we were not towing them, they seem to "Snap Crackle and Pop" a lot less...
I remember working on an L82 Corvette years ago with my pop and we attached the front fenders to the car with the hood on to get the gaps straight, it was cold as hell...four days later we were cutting the ends loose because the hood had a 5/16" reveal all the way around, once the car got to 80* it actually touched on one side...

GT