Some other IMPORTANT notes....
~because of how the TOD works, it requires that all 4 tires be really really close to the same circumference...so you can't (shouldn't) put a single brand new tire on if the other 3 are fairly worn down...changes the circumference too much and MANY have reported hearing some horrible clunking sounds that are completely resolved when 4 equal size and amount of tread (and pattern for that matter) tires are put on.
You do have some lee-way, but many here have had the nasty clunking that it just can't be good for the TOD to do it. It's probably a good idea to buy 5 new tires when you do your tire upgrade. And also keep in mind, the 5th tire must be put into the rotation so its tread wears down at approximately the same rate as the other 4, so when you need it, it's really close to the same circumference.
~Tom4Bren and Marlin have both have their full size spares mounted to the rear hatch door. Both have posted pics in their galleries of the mounting brackets used. Some have said they worry the weight of the tire/wheel would be too much for the rear hatch door hinges. I believe both guys are pretty "gentle" when using their hatch for that reason. I think it looks great personally, BUT, my hatch hinges went hinky on me after 1 day of off roading in Moab in 2009 and I couldn't shut my hatch completely.....somebody fixed it for me that night, but it made me think that I don't want to put any more stress on the hinges, certainly not 77 lbs extra pounds (OEM rim weighs about 28, my tires weigh 49 lbs). My luck, the whole back door would fall off when I'm driving along....
As PK said, those of us with oversized tires, most (like myself) have mounted the full size spare in a roof cargo basket. If you plan that, make sure the cargo basket is large enough to fit the tire. For example, the smaller Thule Xpedition rack 695 that some have, does NOT fit a 285/60-18 tire (pics in my gallery), only the larger Thule Xpedition basket 696 fits a larger spare..see how vt_maverick just mounted his in his Thule basket this week. Marlin cut part of his basket in the middle to allow his full size spare to fit there when he wants it mounted there (see his gallery for pics).
As PK said, if you want, you can remove the backseat and mount it in the back.
Rowhard just finished a mounting system there..check his gallery for pics and the thread. Also, Jolly Roger VX'er, custom mounted his there. http://www.vehicross.info/gallery/sh...275/ppuser/505
I plan on bringing mine down from my rack and laying it FLAT in the back (seats removed) and ratcheting it down in an "X" pattern to the metal floor hooks back there. I'll put it back up in the basket for certain activities, in the back cargo area for other activities.
(Aw geez, what did I just do?...there's at least 4 words in this paragraph that will light up PK...)
~which brings me to your issue....yes, our spare tire is called a "donut" as it's not a full size tire. The owners manual states (somewhere) if you get a flat on the REAR, do not put the donut on the rear. Move a good front tire to the rear, and put the donut on the front....and get to a tire shop very soon. Like PK said, I think 30 mph (or maybe a little more, can't quite recall specific speed), and I think the rule of thumb is no more than 50 miles (but I'd never go that far on a donut personally).