Replying to this thread and joining in rather late.
I think that POW Sides paint their "Red Oxide" wagons with Humbrol No 100. To me this looks a bit too "orange" and a rather unlikely colour for a railway wagon in steam days.
The private owner wagons which I made for "Cheadle" quite a few years ago now, such as Berryhill Collieries, were painted with Precision Red Oxide (as I recall) this to me looks a rather more likely colour for a working wagon.
As an alternative, how about Humbrol Numbers 70 or 113 ?
This thought is based on a subjective opinion, rather than any hard evidence.