Wire amp fan to ignition?

Here recently I upgraded my free air 10 to an enclosed 12 in my 2003 X2. This required me to turn the gain up on my subwoofer amp. Now my amp will get hot and shut off. I bought a battery operated fan and found that just circulating air keeps the amps from getting too hot. So I then bough a computer fan (12v .25amp) and wired it to my remote power on and ground on my amp. I then noticed I'm getting fan noise in my speakers. So all that being said I want to know how to go about wiring this fan to my ignition switch so that when the boat is running or on accessory that the amp fan is running. I'm very new to all this so I'm not even sure how to open the dash or if I can just crawl underneath to get to what I need. Any info will be greatly apprecated.