How about on the floor in the front between your feet, where you can see it and reach it quickly if you need to. Use a little witness wire....think thin brass wire you can break easily, on the latch to prevent an inadvertent bump from releasing it from its bracket and turning it into a 2 lb bruise in the back of the head.
The other option is under the front seat. I prefer to be able to see it. If I ever should need it for its designed purpose I'd rather not be fumbling for it where I can't see it.
Just make sure wherever you mount it, it doesn't obscure your vision or interfere with the full and free range of motion of the flight controls, and PRIOR to drilling a single hole in the aircraft to mount the bracket, check whats under where your drilling as a misplaced hole can do a lot of damage very quickly and be costly to fix.
