Finding the right materials is the difficult part here, you can build a square tube out of plywood if all else fails-there are other sites that provide details of this. The tube you need will depend on the diameter of your mirror cell assembly (the mirror cell assembly will be larger than the overall diameter of the mirror)-The tube I used (200mm dia) is about 7.87", the mirror is 6.25"-PVC or polypropylene type plastics are best-I used a piece of redundant irrigation/drainage pipe-it had slots in it which I filled in with silicon adhesive to prevent unwanted light leaking in. The tube walls are about 5 mm thick-it is very sturdy and rigid.