Since posting this, I've learned that not all Workhorse chassis have 30mm lug nuts. Mine is a W20 with 19.5" tires and it definitely has 30mm lug nuts. If you have the larger 22.5" tires, I believe you have 33mm lug nuts. It's fairly easy to measure your lug nuts with a set of calipers, a metric ruler, or a socket wrench socket. I also read where some W20s were equipped with 22.5" tires so measure carefully.
Here's a link to the 33m version. also on Amazon: