Well been wanting to do this for a few years, just for the fact that I can. Not that it was a huge issue but is nice not having to worry about one of my buddy's latest fling or my wife's friends throwing a towel or bag on top of the amps.
The first one I machined the fins off the side and built two tanks to bolt to the sides of the amp.
Worked awesome but wasn't pretty and permanently made the amp water cooled.
It was pressure tested to 300psi nitrogen overnight with no loss of pressure.
Not the arc amps have the heat sink on the base of the amp.
So I have the other coolers sandwhich to the bottom and are cnc'd out of 1" thick aluminum.
I had to add a few more bolt hols then originally designed to keep it from leaking and these will not hold 300psi. But they will hold against whatever pressure a ballast puppy can produce. Both dead headed and with a large restriction.
I am going to get them anodized over the winter and make the trim panel to hide everything but the centers of the cooling blocks and maybe add a small strainer to the system to keep trash out of the system.
But damn do they work. I had two amps with and two without the coolers at one point. The water cooled felt nice and chilly after 4 hours of beating on them and the air cooled were quite hot.
Also these are arc 300.2's the larger being a first edition so it is slightly larger.