Hey, I appreciate that suggestion. I didn't know about that so I'm going to look at that option now.I have used 12v fan speed controller from amazon before wired inline. May not be what you are looking for but thought i would mention it.
"Exqutoo 2Pack PWM Speed Controller Adjustable Driver Switch Low Voltage DC Motor Speed Controller with Speed Control Knob 1.8v 3v 5v 6v 12v 2A 30W h"