Since I lifted the truck I had a large gap in the new springs because of the increased length. I thought about making my own spacers but did a quick google search and found the Airlift Lock N Lift spacers. I emailed Airlift and they told me they weren't intended to work for this application (they were very unhelpful) but I figured I could make them work. Ordered these spacers from Andrew (at Bully's Performance) a couple weeks ago and got them installed over the weekend. Had to do a little bit of modding to make them work the way I intended them too (cut the lock tabs off the top and bottom spacer) and then I had to drill out the center hole for the bag to go up into properly. Other than that they work great, exactly as I wanted them too.
I got the kit for a 6" lift (even though RCX only lifts the back 4.5") but I did end up using all 6" of the spacers. It just fit better IMO and will keep everything nice and tight.
The one issue I ran into was my airline length... when I first installed the kit I wasn't intending to put them through a 6" spacer before the bag so it was a little challenging getting them hooked up with very little play room.
6" Lift N Lock Spacers