First off, do you have water in the fresh tank? How do you know? Since you have all the drains open, have you added water to the fresh tank and watched if it drained. We sell Cardinal 5th wheel mainly, and the fresh tank is below the fresh tank fill.
The bottom must come off in order, as it is like a tin roof. Good luck.
If you are reading the monitor panel, it may not be accurate.
2012 Ford F250 ext. Cab 4x4
2002 Jeep Wrangler Sahara
2008 Yamaha V-Star 650 Classic
2008 Work and Play 18LT