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Not silicone , it does not last long . Also if you have old tubes of silicone it sometimes will not set up. Sikaflex has worked for me on other parts of trailers
I think this is what I used!
There is rolls of tacky tape they use for sealing around skylights. I got some that was 4 inches wide and you peel the surface wax paper off and it sticks and doesn’t let go, you can purchase it at any rv parts store!
5200 takes forever to cure but its sure bulletproof once it does. Windoweld Urethane is good too. And E6000.