There was a development on this today, and it's not all good news, but hope remains. The local dealer I was in contact with sat down and had a meeting. I may have said this previously above, but not sure (and not scrolling up), the Roll-N-Lock is a no go due to how it mounts at the same location the sportbar does. The Roll-N-Lock retractable cover is 100% out.
Regarding Retrax, they said they could either cut the side rail so it fits around the sportbar mounting flanges, but have concerns it could affect the weight carrying capacity of the cover. They also discussed welding a flange into the Retrax side rails and drilling holes for the sportbar mounting bolts in order to not affect durability. The flame would be sandwiched between the truck bed side rail and the bottom of the sportbar. They didn't want to take on a project they weren't 100% comfortable with, and therefore said they won't do this. This effectively means they are out of the picture, but not the Retrax bed cover.
While considering my options after the above mentioned phone call I remembered what the accessories consultant at the dealership I bought my truck from said when discussing tonneau covers that are compatible with the sportbar. She said there was a retractable cover that worked that GM offers. GM offers 2 brands. One is Roll-N-Lock. The other is Advantage. Hopefully the Advantage cover will work. GM Accessories is currently offering 20% off MSRP for online orders over $500 until June 1. That sounds like a sweet deal to me. Does anybody have the install instructions for the Advantage bed cover GM part number 19416971? If so, any help would be appreciated.