The XJ is running 35's on 5x5.5" Ford bolt pattern while the trailer is running 31's on 5x4.5" Jeep bolt pattern.
I'm thinking about drilling the trailer drums so that they can handle the larger bolt circle as well so in a pinch I could use the Jeep's spare. I carry a full patch kit and CO2 setup. I may just throw in a inner tube for the trailer in in case the damage can't be easily patched.
As far as the corner jig, I actually have two; the good one shown(Bessey) and a HF unit. I don't totally trust the corner jigs. A large t-square and a tape measure are your best friend.
This is quite a bit cheaper