I was thinking of getting the fins under your sheet metal, so they would be in the air above your rear tire, but in looking at your picture cutting a hole and reverse mounting it would be difficult. Probably easier just to bolt it underneath.
Like I said, I don't know how much heat they produce or at what point they fail, but I did have one fail on me once, and it's definitely something to avoid. Maybe some of our more experienced/smarter than me (just about everyone) members can chime in.
You might actually want to post that picture in the modifications page and ask opinions.