I am replacing the shower skylight. My replacement is thicker than the original, but did not come with an inner dome. The original has an inner dome, not sure if I can get it separated from the old...
I would not go with a single. You will end up with raw wood around the inside opening. I have seen the after effects of doing this in an old MH and it isn't very good because all that moisture ends up where you don't want it.