As I'm limited to five posts in 24 hours, I'll consolidate my replies in one post.
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Moe Zhoost, the failures appear to be between the spoke nipples, rather than upon them. The heads don't catch on my fingertips (risky, I know) and your suggestion of a cloth also results in no catches.
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Iride01, the first failure after removing the original damaged tube was on a tube that was listed for 2.1 and larger, although I don't recall the max size. The next and more recent failure was on a tube for up to 2.1 which is what is on the sidewall of the tire. As noted, I'm careful to have no twists or folds, by inserting the tube in the tire and applying low pressure, checking for folds, twists, etc.
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alcjphil, I think your advice has great merit. I'm more accustomed to narrow high pressure rubber; this is my first extended exposure to a fat tire on an upright bike. Another aspect I've forgotten (six years since last riding) is that I apply talcum powder to the tire and tube to prevent friction bonding. At the higher pressure, and no talc, the rubber won't move to "fall into" the locations that are getting bulged. Perhaps a bit of talc and more reasonable pressure will come through for me.
I expect delivery of a replacement tube today and can proceed on my journey.