Shell Definitions keep disappearing

I'm getting really frustrated with trying to do a shell element static analysis.  I have a model constructed of various beams, channels, and pipe.  I have converted them to shells using the offset command.  I then assign a thickness to them as a midplane, assign a material, apply loads, mesh etc.  Everything runs just fine.  Look at the results, decide what I want to change and go back into the design tree and edit the necessary item.  Then go to run it again and all the thickness definitions gone!  Talked with my Solidworks tech support rep and he said that happens because solidworks recreates the shells in simulation everytime you edit anything in the feature tree!  ARGHH!!!!!  Is there a better way to do this?  With 150+ shells of various thickness and the reorder of the shells in the simulation tree appears to be random and different every time you have no choice but to click each item one at a time and set the definition.  Tech support says after creating all the shells, I could then go back and convert them all to sheet metal parts since solidworks will use the thickness definition from the sheet metal definition, but that is pretty time consuming and it visually doesn't work with wide flange beams because of the radius between the web and the flange.  Anyone else come up with a better solution?