Now that looks good, I try to let the PWM area breath as even under load under a cascade I've had the mosfets get pretty warm. The one problem you might have is during the pulldown the evap will suck all the heat out of the board and with no components running you need to be quick and power on to put a load under the evap. With a SS this isn't much of a problem but anything colder and you have to keep that in mind.