I have seen alot of people use melamine board. All depends on how nice you want it to look. Also all you have to do is gett he measurements for the size tub you will use and add for a little room. Also from what I think, the melamine will swell slightly with the heat so make sure you adjust for that about 1/4 inch to keep the tubs easy to slide.

Sorry I dont have any schematics but hope this helps a little bit