Eric has commented and I am repeating the comment as a post since it is easier to find.
So I am about to replace a belt in a Rondinax 60 luckily I have the clip and the belt and know how it is attatched at the hub. I am also about to fabricate belts and clips for two 35mm Rondinaxi.
My comment is you can simplify the hub attatchment by using the original method. Notice the slot in the hub on earlier reels actually has a taper. That is when you look from one side the slot looks abot 3mm wide but from the other it only looks 2mm wide. On the later reals there is a wider slot on one side of the hollow hub and a narrow slot on the other.
The idea in both cases is that the belt is doubled over and pushed through the slot and then a pin inserted through the loop in the belt. The belt is then pulled back through the hub until the pin (around 30mm long and 2.5mm in diameter) wedges in position stoppoing the belt from being pulled any further.
I do like the idea of using press studs or similar to hold the film, I was thinking of making something like the essex has and use a template to cut the film. But a press stud solves that problem (i am thinking for my two 35mm tanks here).
As for the Rondinax 60 i will be using clear PVC tablecloth material at $2 for 0.2 metre x 1.0 metre piece. It is 0.4mm thick and I have just sewwed a small test piece. I will be making an exact copy of the old rubberised version and reusing the original clip.