So much has changed with regard to electric only refrigerators and electric convection ovens and induction cooktop burners and large screen televisions and other "necessities" that there can be no rule of thumb other than more solar and more battery bank capacity is a worthwhile investment. I went from one extreme with a camper with a 3-way fridge and propane oven and cooktop and 200W of solar on the roof to a new motorhome with a DC only fridge and induction cooktop and convection oven and AC heat pump with only 200W of solar on the roof and 125Ah of usable lead acid batteries and so the need to frequently run the generator (my previous camper was without any kind of generator).
With the electric only fridge and cooktop and oven and microwave the use of lithium phosphate batteries become essential if one want to operate off the grid and without running the generator for a couple hours each day. To that end I added 290W of solar panels to the roof and replaced the lead acid batteries to lithium-phosphate ones.
Cost of these two upgrades was $4,000 but for us it was price to be paid for the configuration of our 2021 Navion. But the Navion was one of very few new motorhomes available for immediate purchase in 2020.