The electrical system that I had in my '94 LY included a large alternator (not sure of its size, but there were 2 large chassis batteries (engine was the 5.9 Cummins), a battery isolator and 2 house batteries, which I changed to 6-volt wet cells in series. Because there was a generator, it had an automatic transfer switch with a 60-second time delay relay to allow the generator to be up to a stable 19 volts output before switching over.
I added a 123-watt solar panel and controller, the output of which was connected directly to the house batteries. It worked fine and was great for boondocking.
The caveat is that if the house batteries run low, notwithstanding the isolator, because there are common elements (e.g., the power step), it does draw down on the chassis batteries. I know you'll say it shouldn't, but the fact is that it does. Last year while boondocking near Las Vegas, I had to use my towed car to jump start the motorhome.
I was advised to buy a small generator and a battery charger to use when this happens by other, very experienced, boondockers - since the built-in 6500-watt generator is electric starting off the chassis batteries, if those batteries are low, the only way to start it up is either boosting from a car or using a small portable generator.
BTW, the magazine from the Good Sam club often include a large ad from Harbor Freight. I found the ad that had a 50% discount off their small 800-watt generator and bought it (along with their 2-year warranty) for $110.
1987 Excella 32-foot
1999 Dodge Ram 2500HD Diesel