Tim,

Mike is correct. You will need to setup the breakpoint in order to get the metal to fold (Display) correctly.

Using Tim's screenshot, dont setup 2 lines as he has. Use one line and set the first 2 columns to 99999.
Set your gasket to 4mm or Imperial Equivalent. Then copy the rest. 35mm is the flange size. The remaining '50s are the position of the connector and extension. 
More information here. https://knowledge.autodesk.com/support/fabrication-products/learn-explore/caas/CloudHelp/cloudhelp/2...

A great forum that no-doubt has all of your questions already answered is www.xtracad.com

Double-wall option is used for perforated lining. As this is an additional sheet metal that can be quantified/fabricated. Again, typing Doublewall CADMEP into google will bring up all the information you need.