Most Beaver coaches must be spoon-fed their Cat food very slowly. Most times I am unable to place the nozzle on the slowest fill notch unless I pull the nozzle well out of the hole such that it seems to barely hold itself in the hole. Many times I have to use a long-stemmed screwdriver to hold the nozzle's handle so that it will very slowly fill the tank. I have found that using a car nozzle, as compared to the fast-fill truck nozzles, makes filling a bit easier. Also, tipping the coach over away from the pump seems to help the fuel run more easily into the tank. It can take 10 to 20 minutes to top off a half-full tank.
Our gauges seem to work okay so I've never been into them. I rarely look at the dash gauges. I use the Aladdin and Silverleaf screens for checking gauges.
We leave the inverter powered up. Our coach is almost never without power, either a generator is ON or it's plugged into shore power, and of course when traveling the engine's alternator supplies power. This past Summer I replaced the transfer switch because it had become intermittent when it switched between the generator and shore power. Sometimes it just wouldn't make proper contact to transfer all the voltage and amps. If you have a loud "thud", then your transfer switch may need maintenance or replacement. I know there is a delay built into the transfer system before allowing power into our coach. If you're using a surge protector or have one internally mounted, then they typically have a delay before allowing power into the coach. As long as your batteries are charged, then you should have 12v power because that power comes from the batteries. I believe the inverter only makes 12v power when it converts it from 120v which comes from either the generator and shore power. But that 12v power from the inverter is a result of its battery charging function. That 12v charging current from the inverter is sent to the house and chassis batteries where it is subsequently sent to power 12v devices in the coach. The inverter generates quite a bit of heat and will buzz when it's powered up.
Our coach's outlets (120v) have both circuit breakers in the main panel and a GFI on each circuit. If a 120v receptacle has no power, then either the inverter is not inverting (perhaps not ON) or the coach does not have access to a generator or shore power,... AND/OR a circuit breaker has been tripped,... AND/OR a GFI has been tripped.
Now... so you and others know, my knowledge comes from this Forum and my experience with our 2004 Marquis Sapphire.