How good is thermal epoxy?

[lincpimp]

Making a water cooling setup for a sidewinder for one of my boats. I had planned to use some al tube, cut out some of the fins on the sidewinder heatsink, and epoxy the tube to the heatsink. Looks like I can get 3-4 tube on there, I will either bend them to form a z like pattern or use some tubing to connect straight lengths. My main question is that will thermal epoxy work well enough to transfer the heat from the heatsink to the tubes. Since the tubes are found the epoxy will be 1/16" thick in some places. I am trying to work around removing the sidewinder heatsink, and looks are not really important.

I could also epoxy sides and a top to the exisiting heatsink fins, and just put a pair of fittings for input on output. That way water will be in direct contact with the heatsink.

Before you tell me that I should buy a boat esc, I have all kinds of car escs hanging around, so this is cheaper!