The "literature" is just a collection of owner's manuals for the individual appliances (water heater, refrigerator, furnace, ...). They are usually available online when you look up the model numbers of the appliances. But they will not give a complete overview of the camper system.
In your case, I would check if the battery is in good condition, and if it is correctly connected to the camper. If the camper has been sitting for a while, it is quite possible the battery is dead and can not be resurrected. If, for example, the propane detector has been connected all the time without a regular charge, it will have drawn the battery down after a few weeks.