I did mine on cardboard, and the hot glue at the bottom did stick.
I let it dry and them pealed it off the cardboard and then pulled off any extra cardboard. Once painted it didnt matter if there was some cardboard stuck on the bottom side.
These were so easy to make. I went and bough some more pipe. I hope to find time to make more this weekend.
I found white colored PVC pipe that the tea candle fits right inside without having to drill out any of the pipe. One less step and no power tools required. I think it was a lower grade PVC pipe. The wall of the pipe is thinner.