My understanding is that Silicone is only sealing windows and their frames. Period. I used it on the windows and it works fine. Do not use sulfite as it does not work and will start leaking in a couple years, and be cleaned and replaced with silicone. But silicone is messy stuff, and difficult to both get off the sorrounding window opening (beyond the window frame) and impossible to get of the plastic windows (I guess I should have taped the windows, but didn't).

Don't use 5200 for the fittings if you ever want to get them off. It will take the gel coat off with it (at least that eliminates the sanding). I have had super experience using 5200 as a glue/adhesive that also seals (even when I don't need a sealer - like gluing two rusty cast iron peices together). If I recall, 4200 is a removable version of the 5200.

Otherwise, the word is to use sulfite for fittings, the coaming, etc. I have done that and it works well. No problems and it is long lived.

The problem I have not figured out is that Boatlife products are mixtures of various stuff, and I don't know how their products compare to the 3M and West products which are sulfide, silicone or polysomethingorother (5200).