I haven't looked up Rockstars for our Commander bolt pattern, but i've noticed that most 20" wheels are 10" wide which may be an issue. Check out the KMC website to see what widths and backspaces are available for your bolt pattern.

Another thing to consider is tires. The Commander runs relatively small tires to the rest of the truck world.... finding some nice A/T or M/T tires in the diameter you'll want is going to really limit your tire options, especially when combined with a 10" wide wheel (if that's what they come in).