This is the outside of Bulkhead C. Here trimming can progress right along without problems, as you can see in this picture. You need to alternate between Bulkhead C and Bulkhead D with the clecoing and trimming. Keep a careful watch on Bulkhead D as there is where the biggest problems will crop up at. For me, Bulkhead C went quite nicely. Not so with Bulkhead D, because there is a long piece of aluminum past the Bulkhead and it is going from a larger to a smaller cone. If you do not trim as you go it will end up pulling the skin away from Bulkhead D. There will be many tears shed while you wait for another sheet of aluminum to arrive, if you don't have it already. If you do have it already there will be many tears shed as your scrap pile grows at an amazing rate. Watch your fingers when drilling!!! If you want to know why Patti says that, then click HERE.