In the studies I've done of prototype freight car pictures - it is clear
to me that the interior of almost all gons was "heavily weathered"/worn.
The paint on the interiors did not seem to last very long.
That said - the wear and weathering is much different "in the corners"
than it is "in general". There seems to be a lot of dirt/grime that
accumulates in the corners (any where that two surfaces meet - even
when they are simple over-laps) but that "wear" is much less in those
areas than on the larger "flat" surfaces. In addition, if there is any
deformation of the structure - such as where something heavy has
bent the steel/marred the wood ... those areas rarely have paint
that is intact.
And specifically in my studies of "SP in the 50's" photos ...
I always like to think of weathering/wear as a "process" rather
than as an "effect".
- Jim B.