Forced to move into 5th wheel with issues. Need advice

X2 on the tarps over the top. There should be plenty of scrap lumber around so you can prop it up higher than the roof. That way you'll have room to open your vents when it starts getting warm.

For your gray water tank, if you can see the crack, then I would use some Gorilla tape on it. I'm assuming you have a sewer connection so you can leave the gray dump valve open all the time. Without pressure, the tape should hold until you get into a new place. Good luck.