Paul, I do not have a lot of history with rivnuts, FFR changed that. Previously I designed thread bosses and used weld nuts. When it comes to FRP I am concerned that the squeeze is too high and could damage the plastic structure. I bought aluminum rivnuts for my plastic panels.
On hood venting, my street rod experience with open roadsters is that heat exhausts the louvers and finds it's way into the cockpit. Sides may not be quite so bad but top louver heat comes over the windshield.
jim