I've gone ahead and ordered a BakFlip FiberMax. The Undercover is a 3 section and they aren't replying to my query about how far back the folded config goes so they lose. Since the 2005 GMC bed sidewalls are only 19", hitch head is at 16" and pinbox is 3" you can see the problem. The Undercover is actually recessed so it is flush on top (maybe only 2" between it and the hitch), it probably would have gone back too far.
Although we don't get a lot of hail here, the fibreglass top-surface should keep the snow and ice from holding on quite so much. Should also be more scratch and dent resistant too.
Not too concerned about security... when towing the 5er I use a Stromberg vent-gate (for the cutout). With the Crew Cab, anything valuable goes in the truck (and If I take a genny or bike in the bed it will be chained to one of the cargo tiedowns. I had a PopLock for the standard tailgate but it rusted solid after the first year.
I'm also planning to install an aux fuel tank. With the short bed walls, I'll probably be limited to something like the RDS 37 gallon that is only 9" high. But that might work well with the BakBox that leaves space underneath (which some call a liability).
OC: my revolution would probably have damaged your McGuivered cover on the last trip... even though it looks like they gave me the proper custom wedge for free, they didn't torque the back bolt properly so it was still moving about +/-5 degrees.
2015 Rockwood Signature UltraLite 8282WS Platinum, GY Marathon LRD, TST 507RV TPMS
2005 GMC 2500HD CCSB D/A, Curt E16, Prodigy P2, Garmin RV760LMT w/BC-20 b/u cam