Simple one for me - design it, find some suitable wheels (ebay), have it fabricated and assemble !
Easy !!
Stats :Material - 2mm Stainless
Size - 1.19m x 2.39m
Ground clearance - 40mm
Weight - 56kg (empty)
Liquid Capacity - 140+ litres
Castors - Nylon (With all Stainless fixings)
Cost - £270 approx (Not inc assembly)
Thinking of getting another one made next year.