Hello
If you can PM me an email address that can accept a 10meg attachment, I'll send you some details on how to design a bag skirt that I'm sure will be helpful.
I'm assuming that you are trying to create a low pressure deformable bag skirt which can provide a stabilising moment for the craft, and is resistant to tuck-under. There a couple of issues in the drawings as presented...
1 - the inner radius of the inner section of the bag looks to be the same as the out section - this isn't the case, the inner radius will be larger than the outer radius, and if the system is designed well can be assumed to be straight.
2 - the air feed holes arn't needed. It's more efficient to dump 80-90% of the lift air directly into the cushion, using a splitter plate to divert 10-20% to feed the bags.
If you can receive the file I have here, it will explain more than I can in this short post.
Regarding material, typical 550-600gm/m^2 tarpaulin material is economical and easy to put together - probably the right choice for your project.
Ian