My Flagstaff came with a cover from the factory. They are a PITA most of the time, although sometimes they are useful. It will not stay in place during travel.
Sounds like your dealer is as inept as mine. He probably took it out for another unit. Could do the same for you!
Almost all Flagstaff/Rockwood TT we looked at in 2013 had the cover, appeared to come from the factory as part of the sink.
2001 Ford F-350 Super Duty CC Dually, 7.3 Diesel
2013 832IKBS Flagstaff Classic Ultra Lite, Hensley Arrow Hitch, Carlisle tires
2016 days camped....211, it ain't over yet!
On the road to ALASKA May 6, home Sept. 13, 2016. 23 states, 3 Canadian Provinces, up to the Arctic Circle, 17,300 miles, 131 days on the road. 1 flat tire, 4 oil changes. What a beautiful trip!