I've researched how to make my own engine cowling, and I've decided to do it based on the method outlined in Tony Bingelis's book "Sportplane Construction Techniques". First, I wrapped the engine as much as I could with plastic wrap.
Then, I purchased three 4-foot by 8-foot sheets of 2-inch rigid foam insulation board from Home Depot. The idea is to cut and glue pieces of foam so that the engine is surrounded as completely as possible. The next step will be to shape it with knives, saws, and sandpaper.
Total Time: 13.5 hrs.