I've decided to use a 4" x 20' Flex King Pro liner in my centrally located masonry flue. The Mt. Vernon manual shows insulation only in the damper area, not on the flex liner itself. The Flex king Pro brochure suggests using an insulation kit with the liner. Is insulating below the chimney cap and using a block off plate and insulation in the damper area sufficient? Is the insulation really necessary on the liner? Suggestions please for the best setup. Thanks in advance for any advise/comments. All are appreciated.