Here is my idea. After reading Steve's meanderings on the subject (nice meeting you at the 'glyphs) I took it a bit farther. I added the foil insulation inside from the "burning man" method (I do live in the same county as burning man after all) and added a homemade outside quilt. I had some blocks and fabric left over from the quilt I made for the trailer, so I fashioned a fitted quilt for the ice chest.
My husband thinks I'm crazy, or what he actually said was he would have thought I was crazy if I had actually purchased fabric for this project instead of just using left overs. It is fitted at the back, and open in the front, lapping over the sides to keep the air in. It could have also been made as a "toaster cover" type, but I figured each time I openned the ice chest, it would be to get something out, so my hands would be full and I didn't want to have to figure out how to put the quilt back on that way. so instead it has the open front and is velcroed to the top. Our first trip out, if the trailer gets finished, is Memorial day, so we will see how it works!
Sure, you could put a sleeping bag or wet beach towel over the top to accomplish the same thing, but what would be the fun in that?
Let us know if it works. 
