I'm about to have mine done. Was asking my rigger/surveyor what sealant
he recommended. FWIW, he says that here in Florida
it gets so hot* that butyl will actually get too soft and runny. While something like Sikaflex will hold up to the heat much better.
I guess that might be something to consider depending on your location.
* "hot", of course, isn't so much the air temp as how hot the decks and hardware
get from the hot sun.