Hi Aaron, I’m interested in what tools people are using as well, but I have some info to add as well.
I don’t think flat seams (sometimes called pinch seams) like in the examples you provided are as strong as the lap seams like in a typical packraft. The pressure is more directly trying to tear the seam apart. Here is a youtube video about seams (for pool toys, but the idea is similar) https://www.youtube.com/watch?v=9F0fjaHhgzo
The other factor with this simple approach is that you get wrinkling which is a cosmetic issue and could affect the drag in the water. Wrinkles might be a more likely spot for holes to show up as well. But that’s just a guess. These wrinkles come from the inflation process causing compression in parts of the fabric. To avoid wrinkles, the final inflated packraft shape should be made of what are called developable surfaces. This special class of surface can be flattened into a flat pattern without warping. Cylinders and cones are classic examples of developable surfaces which is why you see the tubes of many inflatables taking on these shapes.
I’m working on some inflatable designs for fun. I’ve been using FreeCAD for making the 3D shape. You can then inflate the shape in Blender with the cloth physics pressure option to get an idea about wrinkling and the actual inflated shape. Blender also has a Paper Model plugin that says it can make flat plans of developable surfaces, but I haven’t got that to work yet. I haven’t found these tools to be particularly user friendly so I’m hoping someone else chimes in with other inexpensive software packages.
-Kevin