Hi,
Hobie has one (again). The original Toybox. You have to buy it from a Hobie Dealer (Sorry, no mail order). It's $364
Another alternative is to use a piece of 24"X x96" plywood as a "floor", then bend a piece of 48" x 96" Type I PVC sheet 1/8" thick over it and screw into the sides of the plywood. It's only $51 Mcmaster.com P/N 8747K213 UV resistant, waterproof, needs no paint. It forms an arched container (like the toybox) 24 inches across (obviously), by about 17 inches high. You can use plywood for the ends, or make the whole thing out of PVC sheet!