I have an 2014 Freight Liner Cascadia. I have a water leak that comes in on the passenger side floor board in the back near the sleeper. It only gets wet when it rains. I have checked underneath the truck and try to seal everything I could. Any suggestions?

Of course it only gets wet when it rains! It's possible the leak is higher up, like on the roof line and running down the wall where it pools on the floor and then you notice it. Or, the water is running down the cab exterior into a seam that isn't sealed properly near the floor. This would not be underneath the truck. What you need to do is run water over the truck in different spots and see when it gets wet inside to narrow it down on where it is coming in. Would work really well if you can dye the water different colors for each time you hit it with water in different locations!

Yep, but start spraying water down low and slowly work your way up higher while checking inside often. Chances are it's leaking at the door weatherstrip or the sleeper vent, not many other places to leak unless the trucks been wrecked and 'fixed'.

i had a situation where the water was coming in from a partially opened upper bunk window. many times, the window locks either do not work or are just never properly locked. check that out.

It obviously get wet when it rains because from the leaks the water will come in and makes it wet.So leak detection and repair is necessary from my point of view.