'03 & '06 CTS's (traded), '14 XTS Lux (traded), '16 CTS4 Premium 2.0T (now)
I picked up one of the Cadillac trunk organizers for the cavern that doubles as the trunk in my XTS. If anyone is interested or curious about these, here it is in place. It does indeed fold flat (assuming there's nothing in it) after you fold down the interior compartments walls. They are held up by velcro straps. The organizer clips to the tie down rings to hold it in place. It seems very well made and sturdy, even though soft sided. I'd say it's Cadillac quality over all. Very easily removable if you need the entire trunk for luggage or whatever. Just un-snap from the tie downs and lift out. I paid roughly $110 for it off Ebay (actually came from a GM dealer. http://www.ebay.com/itm/281587768915?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT ) I'm sure you could find something similar for less but if you want to stay "Cadillac", this is the one.