Craig
Throw the panel on your lawn in the morning at a sunny spot. Place it the crown pointing up, the moisture on one side with the sun shine on the other should
make the panel move.
The trick is timing it right.
This is also dicey The only real success I have had at straightening out bowed panels was done mechanically, and even then you have to wonder how long
the tension that produced the bow will last, at which point your mechanical straightening starts to work against you.
In my shop bowed panels turn into kicks, nailers, and such-usually.
T-bone