I use a cheap caravan water pump picked up off eBay for about 12 quid. It says it shouldn't be used for more than 15-20mins continuously, but I've wired mine to run off a switch giving either 5V or 12V; I use 12V to start for purging any air bubbles, and then switch to 5V for continuous running. It's done quite a few 6-7hour runs with no problem. The pump is in a bucket of water that I change from time to time. I know other people have much more elaborate solutions but simple works for me! No need for fans, radiators, etc, although that might depend on just how hard you are running the spindle.