build a wood frame and fiberglass it to match the area you are gonna install it in. we charge an extra 100-250 for custom f/g battery boxes at our shop and people with nice cars never have an issue paying it. the local competition charges a 300 minimum for anything f/g.
My brother is a master fabricator I could get him to do you 1 for cheap out of brushed aluminum so you can paint it any color you want. or he can do #8 stainless (better than any mirror) but the metal is very spendy prolly 30$ just for the metal. he makes all of our custom amp racks for us out of stainless steel perf and aluminum framing.
Then use a bolt. Just drill a 1/2'' hole in the center of the battery, and bolt it down. //content.invisioncic.com/y282845/emoticons/wink.gif.608e3ea05f1a9f98611af0861652f8fb.gif