A lot of the sedan guys in my area use a double sided tape under their batteries which I think is meant for carpeting. It's not there to keep the battery in the car, just to prevent it from sliding around - they also use strapping tape to secure it. Just a couple small strips keep everything in place.
The tape has a woven pattern, and is thin, but retains a bit of stickiness even after it has been used.
If I can find it on the web I'll post it up.