Hi Andrew,
I didn't say one gate resistor is necessary for each transistor, but the resistor is a good method to get across the annoying traces between the pot and the gate pin.
On the other hand individual gate resistors won't hurt.
Here is a transistor I would recommend for high current. Using two of them is already an overkill for your application. A single transistor can dissipate 306W.
The transistor is PSMN1R6-30PL (NXP-Semiconductors). Check out the attached datasheet.
The colours at the connector outside the board indicate: black=ground, green=+12V, yellow=not used for the fan.
I use that heatsink and fan with an SLA-battery charger and the fan is on whenever the charger is on.
The software I'm using is supposedly the same as you are using. I use Eagle (version 3.55)
Regards
Boncuk