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

As far as the cracked grey water tank goes,clean it up and use JB Weld.Follow directions.I used on on our old trailer's black water tank and it held up for years until we sold it.As far as roof goes,a good silicone caulk usually does the trick.Make sure you clean off as much of the old stuff as possible,Then clean with soap and water.Then make a nice caulk joint and clean up excess.