Remove all the skylights, fans etc and clean up the previous caulk, and tape then put the Eternabond around the area the flange will sit on and use #8 x 1 inch new screws and secure and that in and of itself should form an impenatrable to water seal? Does that sound right?
You really don't want to do this on a roof that doesn't leak. If it ain't broke then don't......as the old saying goes. Now if your were doing R & R and actually needed all those roof fixtures removed and repairs made to the decking then proper way to install those fixtures would be to use the OEM grey butyl tape first and then add a self leveling sealant as OEM. And then add the tape id you so desire.
As others say all you need to do is pull any loose sealant free and clean up any dirt grit per instructions of the product your going to apply.
You need to google several you tubes on the subject and see how the pros (dealers/rv roof techs) do it.
