Your profile shows an Allure 40' 470. You might check the tables for your weight, and find that you can safely downsize from 12R's, instead of upsizing. Or perhaps at least for the front axle. (Our 40' 04 Allure, High Cascade with two Drivers Slides, would allow us to safely downsize to the next size tire down for the front axle. The rear weight, drive/tag, were too close to the top range of the next size tire down to feel comfortable doing so. And I have not done so, as we hope to get another two years out of our 12R's XZE* set of shoes
I also believe I remember reading that another CC owner with with he Continental RV tires, and that they were a bit narrower the the Michelins, for the same size diameter tire. (Memory may be off on this, think it was George B. on the Yahoo CC User Group. You might search via Goole via 12R or 315's and Country Coach - and find more info that way. It's been a topic for well over 10 years, on the options available.)
Michelin TCI centers, and Les Schwab are two tire dealers that keep coming up as being top notch to work with. I've also had good luck with Park House out of Southern California.
Best to luck to you,