I think the thing with racks is you can buy them for the size of the tub your using where as using a premade shelf wouldn't be the correct size depending on the size of the tubs. Premade shelves or book shelves tend to be not that deep. Buying a couple sheets of half inch PVC or 3/4 melamine and building a rack for the size tubs you need would be cheaper even with the cost of flex watt or thg tape.

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