I've got a sheetmetal part I'm designing.  When used in the machine, it will have 3 of these parts end to end.  Actually a gasket will go between them so maybe that does matter in terms of this question.

When I put the part into it's own sub-assembly, I then have to create a linear pattern showing three of them.  My trouble is that I will be fine tuning the overall length of the part and I don't want to go back and change the linear pattern value each time.  How can I link the linear pattern value to something line "overall part length + sheetmetal thickness"?  Sheetmetal thickness could even be a fixed value as I know what I will be using.

Thanks.