Not yet, but I'd like to do something similar (along with a metal sheet on back to supply reinforcement for some mounting clips, and a few other goodies...)
I see no reason why covering it with resin (polyester resin, actually. "Fibreglas" is the mat that is used for a strength member in that particular composite) and painting it would be a problem - just take your time applying the resin, and be ready to smooth out the surface. You'll want to scuff it up a bit anyhow, since the resin can be a little smooth on the surface for good adhesion...
It's also possible to just dye the resin when you mix it, which would save the painting (and if you manage to chip it, it won't show so badly.) Check with a plastics or a composite house for instructions and supplies.
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