Dave:
On planes that will get clear I sand the “Gel Coat”, actually some kind of paint, with 200 grit on a jitter bug sander. If I wasn’t going to clear it I’d probably use 800 wet or dry. The only other prep for the wing, not including the belly pan, is going over the leading edge with spackle to fill any pin holes. No primer just paint. I only paint the area’s requiring the current color. If the plane is going to be red and black and I’m painting red I only paint area that is going to be red. I sand each overlap area with 200 grit to remove any dust bumps prior to laying on the next color. (so when I sand the next color it doesn’t sand through) After all color is applied I sand entire plane with 200 grit and touch up prior to clearing, then clear, color sand and buff. This works for me, keep in mind I don’t use base coat clear coat, I use regular paint for everything.

I paint over the gap tape but as you said the paint doesn’t stick well. If I was going to tape it I would use 3M ¼ inch fine line blue or green tape.

Barry