Making my own drybags luggage. Features?

I decided to make my own drybag luggage such as standard drybags, dufflebags, side bags and whatever else I think I need.

I'm probably going to make them out vinyl coated polyester in a 42 oz thickest. I haven't decided if I'm going weld the seams or weld and stitch the seams. Seems like like most makers just weld.

I'll be using role top only because zippers can leak and break. I want these things to last forever. I may weld on a nylon daisy chain mounting and tie down options.

Are there any features you guys can think of that would make life in the luggage world easier?

We are planning on using dry bags for our trip mostly because we already have them. How did you make out with this project. What is involved in "welding" the bags. We just need to add some extra webbing attachment points and support channels for the webbing to go through. Does it require special tools?