I haven't tested the amp in the car, but it works great on bench tests. The active heatsink I have seems plenty enough for it. I ran it on pretty high levels for about an hour, and the heatsink got to about 55C at room temperature of about 23C. I tried running it without a fan, but it wasn't sufficient. Note that it has a thermal shutoff, and even without a fan, it never reached it, but I decided to add a fan, since the environment in the car gets a lot hotter than 23C. I gave myself a 70C threshold - if it reaches that temperature, I suggest you get a better heatsink.
To attach the heatsink, I used Arctic Silver Epoxy. Works great, but it's VERY permanent. I doubt anything will happen to the heatsink though, and I can change the fan on it if anything.
You'll need a 4x2 header connector, similar to usb header connectors. I bought mine here: http://www.futurlec.com/Connectors/HDCONND8pr.shtml . You'll also need pins for it:http://www.futurlec.com/Connectors/HDPINFpr.shtml
The header is for the input. The output is a screw terminal block, so you don't need anything special for that.
Hope that helps!