Thanks everyone.
Yes it is melamine, and if I could do it all over again I would go with a 3 foot instead of 4 foot wide, I said that as soon as I finiseh it...
But I'm in an area of very low humidity, so the warping *shouldn't* happen as quickly as some climates.
Never-the-less, There are some supports in 3 of the shelves to help that, so we'll see how it goes.
But you're right, I DO need to fill it all up now!!!