I got a smoking deal on a blaze king king this spring (1000 dollars with a class A chimney) but want to ensure good operation, so I'm thinking of changing out the cat and changing the door seal (seems a bit squished and deformed). Is there anything else I should be doing? I think I heard about a gasket that does with the cat. Does this come with the cat? What kind of cat should I get? How about the bypass gasket?