Preben,
You’re welcome, ask anything you wish! The hull framework pieces fit together “eggcrate” style. Measure the slots in the pieces for a clue to the thickness of cardboard. It should be obvious which thickness will fit.
Rearding what Rickstef said, your kit should have looked like
this if it is a genuine GPM, and not a scanned copy. Try to always get original models and stay away from scanned copies, they are always trouble.
Anne