Hi there, cool stuff!
If you need any help feel free to contact me by email - did a lot of custom kites (kite-stuff.org) and some other inflatable structures in the past.
Also, we can offer you our TPU film
if you want to do the welding by yourself or we can make you custom ones with valves depending on your needs.
I'm hoping to construct a new power generation device which needs a kite bladder.
check out http://kitepowercoop.org
for an idea of what I'm up to.
The thing is, I think and great need custom bladders, to inflate the ring.
So I should probably make my own.
Can you give me advice on the materials I need?