Thanks for the tube tip! I've got the awareness of pinching left over from my bicycling days!
I bought a pair of 17" rim strips anyway - just a couple of bucks from a local grump. He says he's used the smaller size in larger rims without any trouble. I found a site that is selling a single size rim strip that supposedly fits 17" through 19" rims, so I'm not gonna worry about it! If I don't like the look of them, I'll consider the duct tape.
I'm really looking forward to getting those tires changed out - the rear one soon, with my swing-arm re-installation, and the front ASAP after that with my fork oil change...