Well for one thing I would NEVER trust a 12" tire for a 650 mile trip! They are far too small and spin far too fast for a long-distance trip. The ones I've used had a speed limitation on them... 55MPH as I recall.
If you have the clearance, upgrade to at least a 175/80R13. Even the 13" tire turns 25% slower, which is much easier on the tire and the wheel bearings. I did that on my small utility trailer and I feel much better about towing it long distances. The tires and bearings arrive cool, when they were slightly warm to the touch with the 12" tires.