re: Planer Table/Cabinet

Mike, I believe that you are going ending up building an apron on each side of your bench,if not this thing is going to flex too much and you will never keep your in-feed and out-feed tables in line.
On each side 6/8 inches from the edge (as to leave like a shelf),I would fill the gap, where you want to put the top drawers, with 3/4" plywood all the way long and glue and screw them in.
That would add a lot of rigidity to your bench.
MY 0.02