Shower Skylight install Idea - Opinions wanted - Henry 887HS

I do not have any opinion on most of the things you are going to do. However I can tell you I replaced 7 skylight over the shower plastic bubbles in the first two years I owned my new Itasca. The plastic dome would crack down in Florida. The factory instructed the dealer not to use screws in the lower flange of the bubble. Apparently it has to be able to move, expand and contract with the heat of the day/night