Oneup's are truly great, better than Thule and Kuat IMHO, I've run all three at one point or another. Can confirm you will need an extender to clear the spare, and consider an extender with drop so that the tailgate will clear the empty rack. Don't rule out the vertical hitch carriers like...
Update with pics and some actual measurements. Extension is about 10.5", drop is 6" CTC. tailgate clears by more than an inch I'd say. I remembered on the ride home that this set up was in place on my wrangler pre-bronco and was just carried over, and luckily worked out just fine.
My 1Up (double w/ two add ons) is on an extender with a drop. Will get a picture later on and post with some rough measurements of extension and drop. Going from my memory only at the moment, extension was needed for me to fold rack up when not in use and clear the spare, and the drop...