I used the closed cell insulation "noodles" made to slip over 1/2 copper water pipes. The wall of these tubes is about 3/8" thick. Use a razor blade to quarter it end to end , and attach it to the shroud with 3M weather strip adhesive. It comes with a peel and stick surface to which will hold it in place while you fit& mock up the pieces. Cheap and worked well on the gap with a factory shroud to Champion radiator.