Just my 2 cents...
I like mine inside. 2 good ratchet straps criss crossed between the tie downs holds it secure even on the worst of my off road misadventures. The drawbacks to me with putting the tire up top is it is a pain in the butt getting a 70+ lbs tire up and down from there (thing solo on the side of the highway someplace)...muck easier to roll it out of the back. Plus, I don't have personal experience, but you have got to feel that weight way up high when you hit the curvies.