Cross sections or Bulkheads

Hi, I have a few kits I am wanting to work on. I'm trying to figure out the best way to get the profile for making bulkheads or the cross sections. I have a contour gage but it's fairly bulky and and not very accurate.
I've tried stiff wire also. I saw an old video of someone making a vacuum form kit and I think he used clay to get the cross section. Unfortunately I can't find it now.
If anyone has any suggestions I would appreciate it.
Thanks,
Michael