I tried a method today to create a customized counterlung. I have used the MRS bags for a long time now and fellow diver in Sweden gave me a good tip that he had found on rebreatherworld. This is how you do it. Take a dromedary lite bag, preheat an iron to the maxiumum heat and firmly press the iron on to the surface that you want to melt for about 30 seconds then quickly remove the iron. This will now have created a perfect seal. You can now customize the MSR bag as you want to. This is great news, at least for me!