There was a Danielle that did a super long ride last week. At least I thought it was a Danielle. I probably have it wrong.

Sprinkle baby powder inside the tire before putting it on. After you put the tube in, push the second bead in all the way around. Then starting at the valve, peek inside the tire at the bead and be sure that the tube is not caught between the bead and the hooked portion of the rim. (You shouldn't really see the tube at all.) Put in about 5 pumps of air, just a few psi. This is the point when the bead meets, or engages with, or interfaces with, the hooked part of the rim. That's what keeps it on. Spin the wheel around a bit, and it should all be OK. Fill it the rest of the way.