Paul,
I never tied these flies on heavy tubes, but I guess that using copper or aluminum would be an option. Personally I'd go for weight in the lower tube the main reason being that the size of these flies would mean adding a lot of weight using a full length copper tube. I also think the concentrated weight in the front of the fly would induce a nice, diving motion.
I don't think the fly would turn upside down no matter what you did with weight, because the wing on the top of the fly would keep it upright anyway. But you'd have to test this yourself.
And speaking of weighted flies: I personally prefer a heavy line to a heavy fly - especially in this weight class. I hate casting both, but a heavy line and a light fly seems to be more manegable than the opposite.
PS: Pete Gray who originated these flies, sent me a new set of pictures showing how to tie them, and I think a whole new article on the subject will find it's way to the site soon.
Martin
