Anyone have any problems with sagging using a 3 ft. shelf of melamine?

I have some 110 qt tubs that I want to turn into display/rack enclosures. I will need a shelf 36in x 19in.

I could use some plastic shelving, but the shelves are 36in x 24in, and that extra 5 inches sticking out from the wall takes up precious space in my small apartment.

Thanks for the insight (and any other you have).