I don't use any.
For the grille, a 1/8" bead of clear silicone on the back side, wait a day for it to set up and then install. It cushions the chrome grille from the paint and doesn't show.
Black rubber on the side grilles just looks stupid...;^)
Yeah, I know that it's a bit (or more than a bit for some) of an eyesore. I need it for several other applications. I'm using a (black crackle painted) Giulietta dash nosepiece, rather than the vinyl covered fiberglass overlay that some have used for dashpad replacement. I like the looks of the simple Giulietta dash - and the fiberglass overlays I've tried fit like the proverbial sow's ear. I.e., not well, for those of you that are not familiar with sow's ears. So I need it for the aft edging of the Giulietta nosepiece, as well as for an aluminum plate I fabricated to act as a fan shroud. PS - NICE Giulia Spider, 101/105Guy!