Did not sand the fiberglass. The original decal protected it pretty well over the years. I did clean it with mineral spirits followed by a scrubbing with ammonia and a strong detergents. Wanted to ensure I got all the wax off. Lots of water for a rinse. Almost couldn't see the outline since the fiberglass was so clean.
The between coats sanding was very light and never got down to the fiberglass. All I want was to smooth out any splatter or maybe a run. I tried not to disturbed the fiberglass. Looks good and passes the 30/30 test. 30 MPH at 30 feet. If you can't see it, it isn't there. I do have some fading on the side that gets sun in the drive way. Might sand it down and repaint using automotive as PRodacy suggested.
The hard part was masking around the compartment doors. I didn't want to see any white outlines so the door frames took a bit of work to mask and limit over spray.