I read this whole thing over a while back and I was going to do the inside of my fiberglass car. I even have some micro balloons I got from an aircraft supply. My main concern was that I could not be assured that I could get a paint compatible surface...clean enough and roughed up enough for the paint mix to stick. Obviously it would turn out to be a mess in the end. So I did not proceed.
I think if you could get a good surface ready for paint and etching primer I'd mix up a slurry of micro balloons and try a small area first. Be sure you use a filter mask mixing the micro ballons. You don't want to breathe any of this stuff.
I'm quite sure it will work.