Cobrajet, I took off one of my tires today and put it in the back, the tires I plan on getting are just a little bit wider, so the plan is to fit three across upright, and then put the fourth either in front of those three (behind the seats) or behind those three (in front of the tailgate)
This of course assumes that all four won't fit across upright
I also have already taken out the back seat, that may make all the difference in the world if you've not done that yourself