For us, we like the idea that driving the RV from Point A to Point B fills up the batteries (it doesn't fill up propane). Also, given conditions, you can stay out longer as solar charges your battery bank (but it won't fill your propane tank).
Lithium and solar provides more flexibility it seems to us. Plus energy produced as a byproduct from driving, or produced from solar, doesn't cost anything unlike propane.
It just provides more flexibility.
Nearly everyone that has one of the big power units, from both the bank capacity and use, says pretty much the same thing. The amount of solar you can put on a B is not enough to make a significant contribution usage coverage. That puts you back to running the engine to get power back if you are off grid, either driving or idling. Lower usage setups, primarily from running propane or diesel for heat, hot water, and cooking can get the power use down to where the solar can make significant contribution and keep you off grid without any other charging source.
IMO, running AC for more than an hour or two off batteries gets you squarely into the area of having a generator, as running the van all the time just isn't what I consider a good idea, and is quite inefficient.
Also remember when you look at charging for the engine, that the 270 or 280 amp alternator is only going to net you about 165ah per hour while driving, and probably closer to 100ah per hour idling, due to heat cycling, so your recharge times can be much longer than what Roadtrek implies them to be.
The charging off the engine is not free. At full output, the big alternator will use nearly 7hp, which is about the same as an Onan, and consume about the same fuel at approximately 1/2 gallon per hour.
Davydd says his ARV uses 100ah per day with no camping use, and upwards of 300ah per day when camping with essentially no AC use. If idling with only 100ah per hour (davydd's new Delco alternator does better), you could need upwards of 3 hours a day. Run the AC, and you will be running the engine well over 50%, if it will even keep up idling.
I understand that some people want to get rid of the propane, but I prefer it for a lot of things over electric or even diesel. You don't use much propane at all unless you are running a generator off it. I don't think we fill up our tank more than once every couple of years.