Tape on alloy mast corrosion risk?

[Renoir]

Stainless steel mast steps were installed over 25 years ago using 3M mylar tape to insulate against corrosion. This worked well because the mast was well painted with the usual green undercoating (a chromate?) and a good paint over that (not linear polyurethane although that would have been good as well, I believe).

The interface between the tape and the paint at the edges of the tape do not provide any egress into the aluminum even with salt water all over the place as long as the coatings on the aluminum remain intact. Therefore, tape against any metal may provide a collection at the edes of salt water that could form an electrical couple yet when tape is against an insulator (a non-conducting paint) there should be no problem.