fill your tires with cement, then you don't need a spare, and you also lower your COG, two birds with one stone.
seriously, when I carried a spare (I don't anymore, I have two tho) I had it on the roof, getting it off is easy, climb up and push it off, getting the flat 36" tire that happens to be filled with Tellico's finest mud back on the roof is where it's a pain in the ass.