I used one like this in the past. There's a little pot on it to adjust the on/off range. Amperage draw may require two or a dual controller. 8/16 amps would be low. SPAL fans are worth investigating too. Their flow ratings are considered more accurate. I have a single 16" SPAL that moves some serious air.
http://www.summitracing.com/parts/der-16749
Dual fan version here:
http://www.summitracing.com/parts/der-16789/overview/