Ah, good that MOSFET schematic is a good one. If you find the MOSFET gets hot, try replacing it with a FDP61N20. It's a similar FET, but with much lower 'on' resistance. So it will run cooloer and let your blowers run slightly faster.
If you're good with soldering, you can replace the on-board regulator with a standard TO-220 size 7805 and a heat sink.