I wouldn't reccommend going to all the trouble of a trailer just so you can carry spare tires. Just bring a patch kit and little 12 volt portable compressor. If you are really paranoid about it, bring a couple tubes just in case you have a bad puncture that a patch won't handle.
I did power tour with no spare, 4600 mile round trip and I did get a puncture. I just fixed it in a parking lot at Abe Lincolns birthplace.