I have a 2016 Miramar with the same kitchen problem. I have been fighting it for 2 years now. Finally, I might have it solved. I first did the latch adjustment which did nothing. The dealer did same thing under warranty, not fixed. I had an upholstery person make a vinyl cover to close off the kitchen and I still had grit getting inside. Finally, I bought some rubber seal gasket from Goodyear Store and ran it along the bottom of the the frame where the door closes below the original seal. It appears to solve the problem, but I have to take another trip to be sure. I will attach some pictures later. It seems that the wind from the ground is getting past the stock gasket at the rear corner.