Ya know, they paint fiberglass boats all the time. If you can't find a
good auto body shop to do it, check with the marine places. If you
want to do it yourself, check into marine paints for fiberglass. No
problem, mon. People always think that vette's are real exotic because
of that fiberglass body, but forget that boats get dinged, fixed, and
painted all the time.

It isn't the painting, it is the prep work.  Many painting a car sand to get
the paint to adhere.  However, a metal body you can sand to bare metal if
you want and unless you are using high speed sanding equipment, the surface
will remain true.

Fiberglass, there is no "bottom" so to speak, and you can sand in dips and
valleys in the surface, so that when you paint it, it looks like it has been
scalloped.

This is why you need someone experience with fiberglass so they don't make
the body look wavy.