Thank you for the advice. It is well received.

I just hand-installed the tire onto the rims. It is a sort of "roll it over the edge" maneuver.

I also checked to ensure the tube was fully encased by the tire and was not trapped between the bead and rim. This was done by flexing the tire at partial inflation.

The rim strips were installed when the tires went on, just a few years ago. So, although they are cotton strips, they are not very old. Even so, this has to be at least a contributing factor, no? I do run relatively high pressures because I am physically big.

I'm wondering if adhesion between the tire and the tube could have caused these troubles. They were quite well stuck together. I feel some talcum powder inside the tire might have prevented that.