Step 6: Attach the Lid (Optional)
If you used a cooler with a hinged lid, skip this step. Otherwise, read on.
By hinging the lid, it makes it easier to open for loading ice and letting air flow in during operation. It also prevents the lid from sliding off and dribbling water out of the heater core while driving. You can use whatever you want for a hinge-a rubber strip glued on, a couple of cabinet hinges, whatever. We used a piano-type hinge that we found in our stockpile of random stuff. It goes all the way across the back, and allows the lid to flip all the way back, but still close completely.