The start the generator suggestion will work IF, repeat IF your on-board converter, charger or inverter/charger is wired to charge the CHASSIS battery as well as the HOUSE battery.
All charge the house bank. Only some charge the chassis battery as well.
If yours does not, and you have a constant on boost switch (vs a momentary switch that you have to hold in to have it active) this will work if you use the boost switch.
But, my suggestion is to get the batteries fully charged, then check the alternator. If not working, get it repaired/replaced.
Getting stranded on the side of the road with a dead electrical system is no fun, particularly if you are not comfortable working with electrical systems.