Has anyone tried these?
http://www.opticalsupports.com/mirror_cells.html
They look well engineered and are quite light. The 12-12.5 inch versions weighs in at about 1.2 Kg only and they look extremely well made. Only thing I'm uncomfortable about is the way they secure the mirror in the cell. There are no mirror clips. Instead, it relies on a blob of silicone fixed on the edge of the mirror with the 3 brackets then tightened up onto it so the silicone flattens out. I'm putting a full-depth 12.5 inch mirror into one of these shortly (when the cell arrives from the maker) and am nervous about whether this system will hold the weight of a 43mm thick cell. They are pretty well priced too. The large size I have ordered plus US$50 or so freight will cost less than A$300 landed so it's not bad. Other positive is that it can accommodate a Cassegrain-style system as well - by turning out a suitable hole in the middle of the supporting plate. There is already a 92mm hole in the base plate giving plenty of room for making suitable connection systems to attach baffles, focusers etc.
Peter.