During summer months we have run the fridge and HW on propane for 3 weeks straight and have not run out of propane on a 20# tank.  A couple years ago we were gone for a month during September in the Rockies and RMNP running fridge, HW and the furnace (a lot) as night temps were normally in the 40's.  Did go through one 20# tank and switched to another BUT the first tank was not full when we started the trip either.

Regardless of that, you will have P L E N T Y of propane for 3 nights, assuming your 30# tank isn't nearly empty when you start.

If you have it running and you are getting an air pressure build-up, that is likely what is happening.

Do not know location of water pump on a 189 however when you find it you will see a small screw off filter on the pump that has a small screen.  That may have crud in it that prevents the pump to work properly, an easy fix to unscrew and clean. 

In the past were you able to get H and C water at all your outlets, sinks, shower, toilet?  If some work and others do not, there are screens at the outlets that may also have small particles embedded causing less than optimal performance or none at all.

Yes, the lower right side of your fridge is the combustion area, you should be able to see and hear the flame.  When pushing the button for propane, did you hear the igniter clicking?  It will make three attempts and if it does not light, will shut down for about 5 minutes before it will allow you to try again.

Basic questions - Is your propane tank turned on?  Are you certain you have propane in the tank, i.e. it isn't empty or near empty.

If you haven't run it there is a good chance you may have spider webs and or bees nests in the combustion area.  You would need to pick up a can of compressed air and blow the combustion area out.

I tend to be on the opposite end of the spectrum as I almost always use propane.  Normally boondock so it is rare for me to even use the 110 option.  Tried the 12v battery option once, that was about 10 years ago just to make sure it worked.