What do you use to seal everything up?

Ok, so that was generic. What I"m actually getting at is, what do you use to seal things like, hatch doors, shore power outlet, outside shower box if you have one, roof fans, etc. I'm wondering if it's best to use butyl tape, silicone sealant or other varieties of sealants? Also, at this point I've refrained from putting any holes in the Filon, but I know when I add these items I will be forced to. I have taken extreme care to epoxy everything. Now what am I to do about the screw holes? These are some of the items I will need to seal up:



