It sounds like your primary control is the amount of time you let the paper sit prior to placing it in the dryer. Or, do you find that you can leave it in the dryer too long?
How long do you let it sit for Crane's patinotype, the offwhite variety? Bergger Cott 320?
What's the placement of your pancake fan within the dryer and with respect to the heater?
Placing the thermostat inside the heater is a good idea. In building my warming bath, I found a thermostat at a Jacuzzi repair shop that controls to just over 110 degrees, and which connects to 120 volt circuits. I could use this device to moderate the heating, plugging the heater into a plug connected to this thermostat. It's adjustable. I think this thermostat was just under $30.
Why did you pick 60% r.h.? (Just curious.) I'm wondering if I can find something that's not too expensive that will maintain a particular relative humidity in my small darkroom? I've been looking for some kind of r.h. meter that I can put on the wall, but haven't found one. Or, have a humidifying chamber of some sort.
Do you use any kind of a filter? My ceramic heater has a filter on the back. I wonder if this would be enough.
Thanks for your response. I don't think this kind of heater would be that difficult to build. I'm a master, when it comes to particle board! Heavy, but it does the job.