Hi Ken, I got this book several years ago. It explains the requirements very well. The book is about $10; I think dehydrator plans are inside. They also sell special heating units but, as I recall, the heating units were more than I wanted to pay.

I made the mistake of buying a plastic dehydrator from a department store. I made some pretty wacky salmon jerky, peanut butter/fruit leathers. A fan is not required if it's built properly. Noise from the fan gets tiresome after a few days.