Tray dryer oven design

I am looking for information on designing a tray dryer oven.
It has 192 trays (640 x 460 x 45 mm)(SS 316L).
Inner temperature required is 350 deg.C
Preferred heat source is Natural Gas. We can opt for HTO (heat transfer oil)
Problem is how to calculate the surface area required to attain this temperature.
Second is how to circulate the air inside. I feel the heat will be transferred to the motor thereby causing damage. For that I am planning to install a cooling jacket on the drive shaft.

Air circulation should be even and slow.

An early advise is highly appreciated.