I think you completely missed the point. Cardboard is a perfectly acceptable medium. Hot glue is not. It is not flexible. Cardboard is flexible.When the shape of the case shifts, the hot glue cracks and lets go. The integrity of the case does not exist. Why spend time doing something with the wrong stuff? Stuffing one piece of fabric in a cavity cannot / will not get out all of the folds which will happen. Hot glue leaves ridges which make wear points on the uke.
Hot glue starts to cool as soon as it leaves the gun. You would hate being in one of my classes. There is a think called a Standard of Excellence. It is yours or mine-- Which ever is higher--not which ever is lower. That some people are satisfied with what they have done does not make it functional or attractive. They pay me to learn how to do it correctly. That person showing his techniques was not a craftsman. Whoever recommended watching it lacked knowing right from wrong about foam-fabric-and adhesives. Perhaps your registered name fits you well.
As I understand it, the site is about learning how to do things the right way. There are all kinds of comments about cheap strings- ukuleles- tuners- and they are to caution people against doing the same thing. That fellow's case making tutorial ranks right close to the top for not needing a blinking yellow light attached, but rather a solid red one.