As I said in my previous post I would go through the whole trailer and tighten all of the plumbing fittings that you can find. This would include the ones to the kitchen faucet. If you do not wish to do this then I would take it to the dealer and let them do it. Loose hose clamps and drain fittings are a fairly common problem with new trailers. I would also make sure you don't have a high water pressure problem and would be sure to use a pressure regulator on your city supply line.
When I was sterilizing the water system for the first time I found the drinking water tank hose did not have a hose clamp and 4 or 5 other water connections in that area were not tight. This prompted me to go over every plumbing fitting I could find and access to be sure they were tight. During this check I also found our sink drain and it's pipe connections were not tight. All of these would result in water leaks that might not have shown up for a long time and likely would have cause damage to the trailer.
One other thing you said you were using the sink for mop water. Did you have water on the counter top? If the sink is not caulked well it is possible water from the counter got underneath and ran down the side.
2015 F150 Ecoboost
2014 Palomini 142 CK