05f1504x45.4

I'm in the process of retrofitting a pair of headlights for my truck with HID projectors all is coming together nicely my question is what should i use to seal the lens back on the housings? some say to use RVT silicone but the doesnt get hard like the glue the lights had before, Some say to use Butyl tape, What is the best sealant so my lights dont get moisture in them.