You say the water is not coming from the drip tube. The material Dometic used for the drain tube becomes very hard and brittle, especially since it is intertwined in the coils on the back of the fridge. They have switched to a black tube material that I think is somewhat better.
For that matter, I went with a friend to look at and purchase a 2017 model travel trailer. He had just sold a too small for them trailer and this was pretty much the right size. In looking over the trailer we found the Dometic drain tube was still coiled up and shoved up in between the coils on the back side, the way it is shipped from Dometic. The factory had never bothered to pull the tubing out and unravel it and route it thru the louvers in the outside vent.
A third possibility is the water is coming from outside via the sidewall vent. It is a poor design and any rainwater running down the side makes its way thru the gap at the bottom where the removable insert and the frame meet, there is no dam or ledge to stop the water from intruding inside.
Charles