A interesting topic to discuss for those who care.
Some of us do remember well, Model Die Casting Company, Roundhouse line of freight, passenger and locomotive "Blue Box Kits".
A few of we old gasers, do remember well, the complete die cast metal kits as well as the semi-die cast/plastic body kits.
Remember how the die cast frames would warp after time on the 40' general service gondola?
How about the 40 foot general service boxcar die cast frame, with plastic body, after a period of time, developing the crack line, below the door opening on each side?
But the die cast frames, on the 50 foot boxcars, do not warp and no cracks belwo the doors, which are fixed to body.
From a physics stand point, why do the die cast frames, warp on the 40 foot gondola?
A simple correction, would be to place in a bench vise and bend back into shape.
Another solution would be to create a series of verticle razor saw and or motor tool cut-off wheel cuts, approximate 1/3 into depth of back of underframe, to , follwed by using relieve stress.
Following this surgical proceedure, with Walthers Goo applied to both metal and plastic surfaces and using "C" Claps to hold in place over night.
Should correct the problem.