I don't know where you're getting your information but I've been doing Vettes for a long time and we never use gel coat and we have a lot of show cars on the road with no fiberglass strands showing.
If you use a fiberglass cloth rather than fiberglass mat you may see the texture of the cloth when the temperature changes but you won't get strands of material coming through the surface.
The pictures below show sanding Polyester Spray Filler (no gel coat) on a 54.
Here is the end result....
We also did the black 57 Vette next to the red one. We did it several years ago and it still looks like the day we finished it. No gel coat on either car.