Like Neil we make do with the inaccurate Bachmann offering - 9ft wheelbase and roller bearings but at least they have the w iron bracing tie unlike some other wagons from that stable. Looking at Paul's site the 9ft hoods were mostly oil boxes.
Its flat tarps for the clayliner isn't it? We have used wide masking tape for the tarps painted grey - not quite 50 shades but looks effective, and folded up in the bottom of the returning empties. Also comes far enough down side of wagon to obscure most branding....
We have changed the coupling on the lead wagon for one with a NEM pocket - the flexibility reduces derailments - and fitted the obligatory tail lamp vac pipe and instanter on the tail vehicle
Usually gets appreciative nods at shows....
https://www.youtube.com/watch?v=AYg23Rj-Pl4
And for gratuitous porn I cant help but put the link to Mike King's photo up again...
http://www.miac.org.uk/images/1048.jpg
Phil