Alright so I actually got this done tonight.
Took me a little while to figure out how to set the rivnuts. Trying to use the tool as it appeared to be made to use, the rivnuts were just spinning in the holes and I was getting nowhere. I took a break and watched a couple youtube vids and figured it out.
I pretty much ended up taking off the nut and just using the spacer and a couple washers with the bolt (so I was just tightening the bolt against the rivnut). Then I put the rivnut on the bolt, gripped it with vise grips and turned the bolt against it a little so it was just starting to expand in the crimp part. Then, I used a hammer to knock the rivnut (still on the bolt) into the hole. By doing this it grabbed just enough that I was able to tighten the bolt against the rivnut and it crimped into the hole flush just like it was supposed to.
Seems strong enough for this application at least. Got everything bolted up and it all looks good.