You can't go wrong with a mark 6! That's my favorite armor. I usually use the Bondo brand resin because that's why I can get at Walmart and is the one I think I hear most people talk about but any fiber glass resin should do.
In order to really harden it yes, you'll want fiber glass it however putting I usually put on a layer of resin first so the paper absorbs it. I use the same resin though.