A very quick and effective way to drive the fans proportionately is to simply connect the fans directly to the smoker rectifier, or fit another dedicated rectifier from the other main drive motor.
As the fans run on such low current they kick in long before the main motor begins to turn, and if the TX is set up correctly it's possible to rev the engine and so energise the fans without the vehicle moving at all, then a little more TX input and the tank is moving with the fans accelerating nicely......or you could install one of Adrians units to do all this for you.
Mechanical engineer.
2 Youtube channels, Phil Woollard and Magpiespyro. Facebook/ Phil Woollard.
Commission builds considered. Pm for my email.