Depends how much they were charging to start with! Maybe it is like
those electrical shops which offer a huge discount, but on some spurious
price supposedly once offered for 28 days at their Rockall branch.
Tank/hopper wagon I really want to make one day is illustrated in (IIRC
Petroleum Rail Tank Wagons of Britain R. Tourret - Tourret Publishing -
1980 - ISBN 0 905878 02 7 ) owned by the splendidly named 'Scottish Fish Oil
and Guano Co. Interesting design as well.