Athearn is running the brown Herzog Thrall gondolas in 15 numbers in HO [this month's announcement]. Of course they have run these in N as well [former MDC tooling]. They previously ran these in the black/red [actually I believe these were former PSCX cars with Herzog added] which are in tie service.
Herzog of course is a major - if not the largest - contractor for railroad maintenance in the US.
See this video for one in action:
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These cars are part of the high tech Herzog Ballast train - which is seen regularly on NS, CSX, UP, CP and BNSF - and probably elsewhere as well.
I strongly suggest you drop Athearn a note [contact us on their site] to suggest they run these in N as well.
This could well be an opportunity for someone to make a resin casting for the ballast doors - if you remember Kelly Cruise did these some years ago.
A side note - why does Athearn not do these in onesy/twosy roadnames for scrap haulers, but hey it would be cool to get a modern ballast train - and it's good for every roadname, which you can't say for the odd ball, mishmash of railroad owned ballast cars out there.