Dave & Heide,
Are you looking for a solar panel that will keep the battery charged after using lights and water pump in the early morning and at night or are you looking to power fans during the day, much use of the pump for dishwashing and showers?
I have two 105 amp hr. Delco Voyager batteries that are kept on a 5 watt solar charger/maintainer. I have run the furnace all night in 37 degree weather, several lights on for an hour and a small fan for several hours during a nap in the afternoon. By the end of the day, the 5 watt has charged the batteries back up with the use of good sunlight.
I don't think you have to have 2 batteries but it sure helps. If you run a number of 12 v. systems during the day then a good size panel, 50 or 75 watt, may power those fans and water pump while keeping the battery up.
'01 2500hd ext. cab, 8.1 litre gas, 5 sp. Allison auto
3.73 rear end
Mag-Hytec rear diff cover
Amsoil Dual by-pass oil filtration system
Amsoil synthetics all around
265 watt AM Solar, Inc. system