Question about tailgate strength/spare tire

I've been looking at various options on relocating my spare, and after being snookered at almost every turn I've decided that the best, most cost efficient option would be to bolt a spare tire mount to the tailgate. Something like the kind that attaches to a RV bumper... (see http://static.howstuffworks.com/gif/spare-tire-mount-4.jpg) Looking inside the tailgate there seems to be some sheet metal 'framing'; I'm just wondering if anyone has done something similar or has any input on the structural feaseablility of this before I start drilling holes in my baby.