I am restoring a 1968 Olds ninty-eight conv with a lot of rusted areas . I’ve been 3 years collecting NOS and replacement parts for it , also several donor cars . Seems the right side of car set facing the ocean . My question is after removing all the seam sealer around the door there is rust under the skin which I cant get out ,other then removing the outer skin, which I realy dont want to . What can I do to prevent this rust from continuing ?