This evening I tackled the 409 bulkhead.It had some oil canning (common at the 408-409 bulkheads), and I had been considering options for quite some time. Finally, I just decided to cut the factory flange off, and make a new flange out of .032 angle. Sort of time consuming, but not diffucult. I fit and drilled the new flange to the bottom skin FIRST, and then drilled the flange to the bulkhead. No gap, no oil canning. Drum tight!