Some news you can use, gleaned from friends and the nature of lead acid batteries.
If you are looking to save fuel, when you charge with an alternator (genset or prime mover) can be important. A lead acid battery will take its fastest charge when it is about 50% discharged. That charge rate depends on the difference between the voltage of the battery (not the voltage of the bus) and the voltage of the charger, which is generally the same as that of the bus. This and the number of amps available, usually limited by the wiring between your alternator and your battery. (Most US RV's have appallingly undersized wiring. Upgrading you wiring is one of the least expensive, most effective things you can do to extend your battery life.)
The charge rate will drop as the battery becomes charged. So, if your goal is to save fuel, that is the fuel you use to spin your alternator:
-- Run your engine or genset while cooking; indeed start it before you light off any big loads like microwaves, toasters, etc. This allows your alternator to take these loads directly which consumes less energy than running down and then recharging your battery. And, if using a genset, has the advantage that most meal times are outside of any quiet hours.
-- Run your engine/genset first thing in the morning, when your batteries are most discharged, for the reasons mentioned above. You will get much more charge for your fuel than if you were to run the engine at the end of the day when the batteries are more likely to be closer to fully charged due to your drive time or solar charge.
