I've had great
seals with 3m 100%silicone 30yr.
If your port is plastic, manufactures tell you only silicone.
If its
aluminum, be sure to use
marine grade silicone, as it has no acidic components which can begin an erosion of the
aluminum framing.
10 people will tell you 10 different products here.
A thing to remember is that eventually you'll want to rebed.
So, if it's easier to remove later thats a good thing.
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