[NH_Bulldog]

I have the same floor cutout under my drain (it is a standard p-trap). Typical with RV manufacturers where nothing is precise, all openings tend to be much larger than necessary. At least yours has the Darco covering in place, mine was a big open hole to the underbelly space. I had the Coroplast opened for some other work at one point and screwed a piece of plywood over the hole from underneath. We don’t camp in cold weather so I am not worried about the lack of floor insulation in that area. The floor doesn’t have much R-value in the first place, especially considering all the other holes and openings.