Attach with Velcro, or as in this case, bungee cords. This power supply is a twelve volt battery used for cell phones, portable computers, and other applications. At the May 2000 Riverside Telescope Maker's Conference, Bryan Greer presented an impressive series of videos that showed light reacting to the temperature differentials in a mirror and tube. However, the video was much more impressive than the magazine text and accompanying illustrations. It was amazing to see how much the temperature in the scope and mirror affects the stability of the view.
Materials generally expand as they warm and contract as they cool.
Unless the mirror is exactly the same temperature across its surface and throughout it's depth, the mirror will have some relatively expanded areas and some contracted. If a precision polished curve is differentially heated, then, the curve will change, and probably not uniformly. But even more dramatic is the effect heat has on the air in the tube. That disturbance propogates throughout the tube. Looking through the tube, the observer sees the same phenomenom that one sees looking at a distant object over the hot pavement of a desert road.