On Sunday, April 10, 2016 at 7:17:01 PM UTC-4, dadiOH wrote:
DerbyDad03 wrote:

Groove or on top of a batten? How is it attached to the sides? In
either case, how much do the sides extend below the bottom?

Grooves in the sides and front. The groves extend about 1/2" below the
bottom panel. The bottom panel is now kind of bowl shaped, sagging
left
to right as well as front to back.

Simplest fix is 3 screws through the bottom into the back. Put one in the
center first, then one more on each side halfway between center and side.
That should fix the sag in both directions; if not, slack off the last two,
add another one (two more total) between them and center, then tighten the
loosened one.

Ah, if it were only that simple. To repeat what I just posted in response
to dpb's post...

I clamped the bottom of the drawers to the back of box in three spots,
completely closing the gap along the back. The front and sides of the
bottoms are fully seated in the grooves of the box. I placed a 36"
straight edge across the bottom of the interior of the drawers and
measured the gap between the straight edge and the bottom of the drawer
at the center of the bottom.

3/8" on one drawer, 1/2" on the other.