There are two fuses, one in the rear power bay, and one in the front power bay with the charge relay, which you need to check. They are big black fuses with a cover. See my attached diagram, they are shown on either side of the charge relay. I carry a spare fuse which I ordered jic off Amazon, but you could probably get at Napa or other store if in immediate need by calling around. Mine are Bussman 400 amps and I would suspect yours are the same, but could be either another manufacturer or 300amps. The fuses are marked with mfg and amperage, which you'll see when you open the top cover.
With your described symptoms, the problem is either one of the fuses (most likely), or the charge solenoid itself not working (less likely). Either one are easy fixes.
You can easily check with a cheap digital DC voltmeter. With engine off and batteries at rest, the charge solenoid will be disengaged. You should have somewhere around 12.5 volts on each battery side connection of the fuses. If the fuse is good, you should also have the same voltage on the other side of the fuse. If you don't, the fuse is burnt, replace it (after disconnecting the applicable battery bank from power).
If both fuses turn out to be okay, then verify the the respective voltages are on the big terminals of the charge solenoid. Then start the engine and the chassis voltage should jump up to about 13.5 or more (showing the alternator is charging the chassis battery). The charge solenoid will engage, which should then provide that same 13.5+ voltage on the terminal going to the house batteries. If it doesn't, your charge solenoid isn't working.
I'm not at my coach to get the specific fuse, but it will look something like this (inside the cover):