watched a program on tele today about “How its Made”. They subject was “Chemical Tank Trailer” youtube.com/watch?v=g4BiI0JsnR8
I remember collecting new tankers from WP Butterfields Shipley about 1972 and some Clayton Tankers not a lot has changed in design.
gracesguide.co.uk/W._P._Butterfield
claytoncommercials.co.uk/index.php/about/
Regards Kev