I use a first generation Popcorn Pumper for roasting.
Its built very well, very heavy duty, and has a strong fan so capable of roasting a large batch size for a popcorn machine.
First change I made a long time ago was to bypass the internal thermostat so it would not shut down at too low a temp.
Then I added a 2nd power cord, so I have one cord for the heating element, and another for the fan.
Also installed type k thermocouples as shown in the pictures below. Finally I insulated the heating chamber.
Next to the chamber, I added a layer of Silicone Rubber, glued in place with high temp RTV.
Mcmaster # 8632K421
1/16" Thick, 12" X 12", 40A Durometer Extreme-Temperature Silicone Rubber (Same as 8632K42)
2nd layer of insulation is a layer of foam.
Mcmaster # 86145K21
Melamine Foam Insulation 24" X 48", 1/2" Thick, Light Gray
Shows thermocouple wire exiting through the silicone.
Environmental (ET) thermocouple probe placement, where hot air enters the roast chamber.
Bean Temp thermocouple probe placement.
Drilled hole in plastic in side of Pumper to insert the probe as shown.