UPDATE:In exploring the potential causes of the bubbling the mfr. suggested "heat from the sun" as a possible explanation. We rejected that because bubbling such as that shown in our photo would be a widespread, very common problem in RV roofs should heat from the sun be able to cause it, and because an insurance adjuster said it wouldn't be caused by the sun.
The mfr. seems to have been right, however, about the heat part, anyway. When they mentioned heat we were reminded of a fire back in 2019 that had occurred in the storage yard where I keep the RV when not in use. While there was no visible damage to the RV other than soot and discoloration marks on the roof from some embers that had landed on it, the front and rear of the RV did get exposed to heat from the fire.
When the fire occurred we filed an insurance claim with NGIC (National General used by Good Sam) and they paid for cleaning of the soot left by the fire on the RV. A few days ago I emailed NGIC requesting a new roof, and without any fuss at all they agreed!
We had documented our request well with photos, and we told NGIC what the adjuster had said. He was the original adjuster on the claim when the fire occurred, but he had moved since then to another company. We knew where he was and reached out to him, and he was willing to speak with NGIC on our behalf. I don't know if they contacted him or not, but in any event NGIC is making good.
Thanks to all who took the time to read my query and of course those who replied.