go to Walmart and get a deep cycle marine battery and plastic housing case. Go to a real hardware store and get 4 nylon bolts and 4 nylon nuts. Go to Sams Club and get the gigantic power inverter. Drill holes in top of plastic housing according to hole positions on inverter. Use nylon bolts to secure inverter to the top of the battery lid. Drill/cut big holes in back of lid to fit wires through to battery terminals.

Done.....total cost, around $120. Should be good to power a large fan for the entire day of racing....on top of the battery charging needs.

Con: heavy
Pro: super easy to replace battery (3+ years and I haven't had to)
Pro: so much power it could power fan, charge, jump start your car, power a light at the same time for 8+ plus hours of heavy duty usage.