[DmaxDually]

I'm going to be replacing the plastic exhaust vent cover on the side of my RV for the microwave exhaust fan because it has turned yellow and stands out like a sore thumb against the white gelcoat. I scuffed up the new cover and painted it using white Rustoleum paint for plastic to keep the UV ray from fading it again.
My question is what is the right sealant to use when I install it? Silicone, acrylic, butyl, Dicor, Butyl tape, etc?