They were designed to use butyl. I like the ribbon stuff around it and the caulk gun goop under the front. I did add urethane under the edge against my glass after it was in place before I zipped the lock strip in. We did not do the urethane on Hoppy's, and his did not leak. I have seen some saying urethane is required legally, because it has to be bonded (which butyl does not do). I know some guys say they have them in with no sealant, Maybe OK on the glass, but I would require something to the metal.