I would be skeptical of a 75/100lb box being held down with nutserts if you were ever in an accident.
It's no different that a 3/8 nut and bolt. Just the nut is swished on to some sheet metal.
Also be careful to drill the holes just large enough to fit the rivet nut.
I made my own tool before I bought one. It worked fine but was inconsistent and way more work than the real thing. Plus I had to "make" a tool for each size I wanted to install. The actual tool takes no more time than a regular pop rivet but can produce repeatable results and is easily adjusted. Worth every penny in my opinion. But Ive installed a ton of nutserts across my projects. I use them whenever I can.Old thread, thought this was a good idea for a tool to set nutsert/rivnut.