Keep it square.

This may look like taking an axe to cut balsa wood but hang on!
Card models need to be kept square and so this is where a hefty lump of iron- yes it is an iron- comes into its own.
this ensures that the card and its bracing stays where it is supposed to be- nor warped!
So as long as the object is kept square then the weight will make sure of it all staying in line- Plus it stops me having to do the ironing or light the fire!