ORIGINAL: Bax
What do you mean when you say ''flexing fuse''? Do you mean that the tail wiggles from side-to-side as the model flies? Or do you mean that you can squeeze it and feel it move in and out as you squeeze and release? The first should never happen, the second happens with almost every molded model out there. Make it too rigid and it's too heavy.
Bax,
That's why many of us that craft our own fuses resort to composite lay-up. Not only is it lighter than glass-epoxy alone, it is far stiffer.
Glass alone would produce the fuse you describe ("oil canning")