I used one of
these from Tractor Supply. I also have a rack but this way it's available for times I don't take the genny without having to unbolt the box.
The piece that slides into the receiver is short, ignore the picture on their site that shows a longer one. I had to use an extension to get it on the Curt front receiver on my Chevy. The extension is only 8" but that helps move the box away for better cooling.
Depending on the thickness of your box (mine is kinda thin) use some healthy fender washers on the inside of the box to distribute the load and avoid stress fractures.
