From my personal point of view, fans are great to use when you don't have enough heatsinking. I don't like to use fans and only use them when I have no other choice.

I think that the best way to mount the Quark is to the chassis. That's about the biggest heatsink that you will have available on an rc car/truck.

I have a bit of an odd Quark setup. I added an additional six capacitors to my Quark. The capacitors are contained in an aluminum box which is roughly the same size as the Quark. I epoxied both the capacitor bank and the Quark to a 1/4" thick piece of aluminum and then mounted that to an aluminum plate. The aluminum plate is attached to two aluminum standoffs which attach to the chassis using two of the stock engine mount holes.

This setup added a bit of mass to the Quark case and effectively transfers heat to the chassis. I don't run any fans on my setup and don't have any thermal issues.