On Sunday, April 10, 2016 at 12:29:09 PM UTC-5, DerbyDad03 wrote:

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.

I suppose your last option may be to remove the panel, moisten the raw (bottom) side for a day or so, then allow to dry in a "clamped" reverse curved position (over correct the curve, a bit), to correct the bowing... and hope that does the trick. I would suspect the wood is air dried, but sometimes old "cured" air dried wood acts as if it's kiln dried and is not always as bendable/reshapeable as new/newer air dried wood. I don't think you would damage the panel if you gave this a try.

Sonny