The example I worked from used cleats down the length of the front and rear rails. Having had some experience with MDF sagging I chose front to back supports. There are four front to back supports 1 1/2" x 3" on edge making a total of six supports including the leg pieces. The trick here is to miss the dog holes ;-)
Pocket holes and glue to attach at the front and rear. Recessed 1/4" lags to secure the top (not glued). This method of top attachment allowed me to shim the top (like you might do with a router table) and get it as flat as possible.