I did the same. Hard to do when you have mixed front/rear like us. I've got the same size wheels you do. I planned to just bring a can of Fix a Flat with me and if one goes I stop and have it fixed. I do have an extra pair of 17" front wheels that the tire place scratched up I could use.
Also I love the build, you're inspiring me to work harder at getting mine done.
Riddler