I used Aluminum....
Hi Dirk,
I started flying the Val with just a lousy spray-paint job on the inside of the cowl. I used a high-temperature white paint, and it did not give a hard or smooth surface. With the inevitable drips and drops of oil, I could see I was going to eventually have an unpleasant mess on my hands, so Purchased a couple yards of the sticky-back aluminum foil that Van's sells. In addition, I bought a roll of aluminum tape from Home Depot Aviation Supply, and went to work. I found that the first thing I had to do to get either types o foil to stick was really clean the surface using white gas (Coleman fuel). That got any remnants of grease off. Then I used the big sheets of foil where there were flat surface, and strips of tape when I had compound curves. You need to use a stiff plastic scraper (like you'd use for Bondo) to really press it on well and make it conform. It probably took about four or five hours all told, but now I have a surface which is smooth and impermeable to oil - easily wiped off.
In retrospect, I would recommend a good, hard and smooth paint finish or the aluminum foil treatment from the very start. It's easier to do while building than later on when you'd rather be flying.
Note - several folks have asked if I noticed a change in engine temps after the foil treatment, and the answer is "no". I only did my lower cowl for now - will do the upper some warm and rainy day (rained all day today, but to chilly to do good work in the hangar!).
Paul