On that model you don't need 12V, it'll have piezo ignition, which you should be able to hear ticking when you push in the ignition button. For gas you need to ensure the cylinder valve is open and that the isolating valve under the kitchen is set correctly. Gas burners of that age often suffer corrosion which blocks the supply. If the hobs light then either the isolator is wrong or there's a,muck issue in the burner
Caravan fridges only run on 12V when connected to a car, the 12v part coming from the car's alternator, not the caravans battery.