Another way of thinking ... that to many probably seems to be off the chart thinking ... is this:
Assume your RV is also sort of a disaster scenario escape module. For that, you need it to be configured to have as many self containment options as possible, or as you can afford. Since you have a large built-in main engine along anyway, a good sized alternator always on tap spun by it adds nicely to those options.
FWIW, we keep our rig stored in the back yard with - as much as possible at all times - all tanks full that should be full, all tanks empty that should be empty, and all batteries full that should be full.
Of course solar (which we do not have) fits in nicely with the above options thinking, too. I've so far procrastinated my way out of adding solar to our rig, as it's large alternator and two generators have muddled my thinking. ;)
By the way, being "always prepared" makes it super easy to get ready for each routine RV trip.
P.S. We are right now in the 35th hour of a massive power outage. The DW slept out in the RV last night with it being kept warm from an electric heater that was powered from a house outlet that was kept active via our emergency 4400 watt whole house generator.