Okay, if recoating is one of the options, how about welding studs from the outside to the inside (the studs would protrude inside, ground flush on the outside). Then have equally clocked L or J shaped slots in the baffle collars so that you insert the baffle and give it a twist to lock. The addition of a mild stainless spring at the end would give you a preload to ensure seating. In addition, to ensure the baffle can't be blown out, and to add more sound baffling, put a bolt on turnout at the end.