I have 107 doors in my storage facility. All 14' tall. No issues with clearance as in California, the vehicle max height is 13'6"
If the door is balanced properly, any door opener will be just fine so long as it travels 14'.
It would seem that if Tiffin lives up to its reputation of standing behind their product, they should have those decals available.
Whether or not they provide them at no charge is maybe a dream.
Regarding removing the old decals, like what was mentioned, it can
be done, but there is no "easy" way to do it. Probably a gentle heat gun to soften the adhesive and a plastic putty knife. I have heard that Goo-Gone removes the residual adhesive. I have used Crud Cutter as well. Both are available at Home Depot.
Regarding Yosemite, you can find spots as there are cancellations all the time, but you have to be johnny on the spot and hit the Reserve America website several times a day. It can be done, but you have to be flexible on your time.
The drive up Hwy 1 can be a bit of a challenge, especially around Big Sur. It gets narrow and curvy. Nothing that cannot be done, but it is a challenge.
Take your time, pull off often, and try not to sweat the time factor.
If you decide not to try Yosemite, there are literally dozens of campgrounds around Mammoth lakes that rival Yosemite. Granted, you don't have the Yosemite Valley, but there are plenty of other options. Fishing, horse back riding, devils post pile, Rainbow falls, endless hiking possibilities, good food in town, free shuttle buses, nice camp grounds.
While I love Yosemite, it is a bit of a zoo. Tour buses, crowds, overly eager rangers staring you down. If you have a dog, expect to get a lecture about leashes, potty bags, yadda yadda yadda. It's frankly overdone, but just the same, beautiful.