It might be worth considering the hinge-top snap caps as a finishing touch, in addition to the rubber shims/washers, which will help protect your paint from chipping.
I got my snap caps from McMaster-Carr. They are available from other sources as well, in a variety of colors, including Chrome and Gold.
I'd suggest using stainless steel screws so the heads don't corrode away over time. The last thing you want will be to have to wrestle with screws whenever you want to dismount the visor, like if you have to have your windshield replaced. There are screws with broader heads called truss head screws which spread their clamping force over a wider area. They work really well with rubber washers to prevent cracking of fiberglass.
Here's the link to the McMaster-Carr Page:
https://www.mcmaster.com/Snap-Caps/hinged-fastener-caps