I think it depends where and what you are mounting. I use well nuts to secure my windscreen onto the fairing. For the actual fairing to the bike/frame I use the oem brackets and hardware. In 1 spot I fabricated a piece of sheet metal to help hold the belly pan up and next to the frame.
H Hell, i've tapped the frame for an L bracket to hold the upper fairing on a GSXR . Those white derlin inserts for race bodywork just don't cut it half the time.
I usually try to make a bracket with a dzus fastener instead of bolting fairings directly to something. The fiberglass lasts longer and it makes it easier/faster to remove the bodywork. This works for the lower fairing most of the time. I don’t care that much for the front fender and just bolt it directly.
Take a look at McMaster and search for well nuts. Size can be a problem but you can use a few wraps of electrical tape to make the O.D. a little larger. We use the 6mm for mounting fairings on our GSXR 600's (2006 & 2008) in the frame and other locations. https://www.mcmaster.com/well-nut-inserts