Makes sense to use an extension rail. The issue then is making bellows that don't sag, and 2 or 3 ring tabs can help enormously.
Originally Posted by tim k
I'm about to make a set of large bellows for a De Vere Monorail and looked how the originals were made, as well as those on my two Agfa Ansco 10x8's as all have very minimal sag. While the stiffeners on the original De Vere bellows are quite thin it uses three cloth layers this seems to give the additional stiffness preventing sag, the original bellows would have been made by Camera Bellows - now Custom Bellows in Birmingham, UK.