No matching spare on my H3, it's under a black tire cover. The 305/50/20 is close to the 32" diameter of the stock base Goodyear tire, so it will work fine as a short term spare.

Yes you are correct that a spacer is required to but the larger wheel/tire on the back door. So that means in case of a flat on my rig, the flat tire will have to be carried in the rear luggage area until repaired/replaced. I keep an old blanket in the back for carrying dirty stuff like that.