Just want to pass along a new leak mode that I discovered in my camper. I have the mushroom vents that CLC sells. Originally they screwed shut to keep out water, which they did very well. The problem I had with them was that when the were unscrewed for ventilation, rain running down the curved camper front would enter the vent and cabin. I was woken up by cold water on my face during a thunderstorm. The vents at the back were OK because of the overhanging galley.
It turns out that the vents actually have a cylinder that fits on the inside and is open on the bottom. This was not originally part of the construction process. Installing those as part of the vent allows air from underneath to enter while blocking water from above. It also eliminates screwing the caps open and shut. They are always open. No more leaking during thunderstorms, no more forgetting to tighten the caps before driving and having them fall off on the road.
However, as well as they work for driving and camping, it turns out that at the car wash water can find its way into the bottom of the vent and from there to the floor of the camper. I just finished mopping out my camper and have the mattress out in the sun drying. Just wanted to warn everyone else who has transitioned to the full mushroom vent to be extra careful when washing your camper and check for water afterwards.