have you looked here;http://www.cleantech.co.uk/catalog/index.php?cPath=22_25pretty reasonable i think.craig
http://www.btowstore.com/epages/Store.sf/?ObjectPath=/Shops/15094/Products/Tnk250uOR IT'S 50 GAL OIL DRUM FOR A £15 FROM THE SCRAP YARD AND GOD KNOW WHAT BEEN STORED IN IT. Don't be a cheap skate get a proper baffeled tank for your van and fit it well, 250ltrs is 250 kilos thats like three prop forwards hiting you if you have a crash. i.e you would be toast! and a bit wet as well