The channel locks may mark up the anodized surface. I know of some who have used a large crescent wrench (very carefully). The cap is usually not that tight. I personnally made a wrench from a small piece of aluminum plate. Simply marked shape and size on plate, drilled holes at each corner and cut between. It's not pretty, but works great. I also beleive there are cheaper sources of this tool on the market, although don't know the name offhand.
Hope this helps.