Your choice
Jim,
You can go either way. Rubber seal alone, proseal only, or a little of both! I am sure that is not the answer you are looking for, but most likely the one you are going to get. You are going to hear from guys who have had luck with the rubber gaskets and will tell you to use only them and it makes removing them so much easier. Then you are going to hear from guys who have been battling leaks and will tell you to trash the gasket and go with proseal.
My left tank (plagued by leak) has the rubber gasket with proseal! Absolutely no leaks what so ever! It is easy to remove, as having the rubber gasket allows you to get a small knife blade in and cut the proseal! Can be removed without removing the tank. (RV-6A)
My right tank (No issues at all) has just the rubber seal. Be careful not to overtighten the screws as you will induce problems.
It is your call, you can't go wrong. If it were me (remember I have been doing tank leak repairs) I would use the gasket and proseal. It will not leak!
Long winded, but there you go!
Dan
