Ron's tank mod is awesome, If you have a decent fabricator in your area, it would be worth having that L channel bent and welded in, that closed cell dense rubber is gonna outlast everything I've seen to date, there is nothiing to cut, the flat of the lid mates against the flat of the channel/gasket.
Did Ron say that BLUEline was doing this NOW? Then you could order the ring and have it welded in locally, like my Reel Splitter.