FWIW, I once had problems mounting a latex tube when I tried to finish at the rim joint. I was used to mounting sew-ups by finishing opposite the valve and the thin tube kept getting trapped under the bead. I couldn't finish pushing the tube into the center without risking a tear. I had seen advice to finish at the valve and thought the advice was crazy.

What I finally figured out was that I could get the tube in by starting at the joint and working back to the valve. When I got to the valve, I could push the tube back into the tire with the valve, then finish with the bead.