Jct

I don't know which one is lightest. But I think much has to do with the paint preparation, and the application of the many coats needed to get to the projected finish.

Glass and epoxy, I have done a few times, it is nice but heavy.
two coats of epoxy, sanding, primer, sanding, application of panels line, final primer, base coat, colors, markings, stripes and then clear coat. On a TF P51 giant, it added up 3.5 lbs. But it is nice. 26 lbs dry. 3w60 for power.
I am working on a different project now. I am trying Koverall and paint in an effort to do away with the epoxy and a lot of sanding, and also save some weight.

Glass and epoxy up to a point can add some strenght to the structure if heavy enough but then it weights even more.

Ray