Just wanted to point out a couple of recently completed auctions on GunBroker for U.S. Model 1200 trench shotguns. You don't often see these coming up for sale, and I think they are under-appreciated by the collecting community at the moment. The 1200 is still in military service, so finding them "loose" on the secondary market is rare indeed. I believe these will become more collectible with the passing of time, and we will be reminiscing about "the good ol' days" when they were selling for around two grand. These 1200's are the end of the line for U.S. combat trench shotguns in a traditional sense (handguard/bayonet lug).
Both of these are from the later run, and appear to be in decent shape. The gov't has surplussed some of these to PD's, and they end up getting sold or traded in when the PD's upgrade to a more modern platform. The early ones have a black anondized receiver while the later ones are gray like these. Enjoy.
http://www.gunbroker.com/Auction/Vie...Item=435418494
http://www.gunbroker.com/Auction/Vie...Item=444193761