Yep. Pan head or hex head is what I want (I called pan a dome head, sorry).
Found an amazing place for fasteners in Vancouver, they only carry SS. When I told that needed "deck screws with pan head" they said: "There is no such thing, who would need deck screws with pan head"? :)... Asked them to give me anything of that size with pan head for wood or plywood, and they brought me screws that were identical to sheet metal.
Will check West Marine stores, thanks - I don't like them, trying to buy elsewhere.
Rob - yes, I'm using well nuts inside. Don't want them outside, not because of leaks but because it gets too hot for too long time where my rig is, and rubber don't fare well when it's hot.