We are currently in the shop for the same issue. Our grey water smell was coming from under the rig and being pulled into the RV through various openings. Turns out that a cap was never installed for the washer/dryer drain (we did not get the washer/dryer option) and the p-trap for the washer/dryer emptied of water. Since the drain was enclosed from the interior by a wall, the smell found its way outside through some openings in the bottom of the compartment and spread its sent all around our rig. We are getting our rig back today. Hopefully, this resolves the problem. Good luck with your problem.