Ronco Plastics...
They make TOP quality, thick-walled roto-molded tanks, and have more than 400 shapes and size--over 100 of which are non-rectangular--to choose from..and for a VERY reasonable price. I'd bet they have one that will fit your space. And you can spec your own fittings sizes and locations, to be installed by them when the tank is made. Their catalog is on their website at: http://www.ronco-plastics.com Delivery is two weeks or less.
