Thanks guys, you excellent advice has given me some ideas.
Zerogee - you are correct, 4 wheel Euro style, painted one solid colour (blue and/or red) with custom artwork/transfers/decals. At least one, probably several, and in an ideal world delivered complete, but not adverse to making them up myself.
Have now located a source for the tank wagons, and am contacting Chris Moxham regarding the custom markings.
Unless you guys have any other ideas?.......