Made a similar but thinner one for my son. He tried it out with a belay on a short rappel. He uses it everyday to carry his possibles.

Used 1" tubular climbing web, Dynema thread and one of these 4000 lb double pass buckle . Of course there is super secret special hidden knowledge one needs to sew such a thing and use it safely.

One of my friends uses one when he skis the Haute Route. It functions with leg loops for crevasse travel and to hold up his pants at the Discos at night.

I noticed "The Belt of My Dreams" is made of polyester. It would not be as dynamic
as some materials.

Video on two other sling materials tested to failure.