Don't know anybody with an Avalanche, so query for anybody who has or knows how it works. Does the "mid-gate" only have a single position, i.e. if you take it down is the cabin exposed to the elements from the rear, or can it be put back up in multiple positions, to enclose a 2-seat cabin and long bed? Or have I totally misunderstood the pictures of how the thing works? If it does leave the cabin open on an Avalanche, any chance they're changing that for the Silverado?
The Silverado EV has a 60/40 Split in the Midgate and leave the Window up to enclose the bed or you can put the whole thing down.
I had a Chevy Avalanche. It was a great vehicle and really liked the versatility of the mid gate. It was not a 60/40 split but the window came off too, so you could use the entire opening. This why I have a pre-order deposit in for the Silverado EV. They should have called it the Avalanche EV though.