Have you tried the Aux Start Switch? I don't know how your Fleetwood is set up but even if our inverter is left on, it will only impact the house batteries not the chassis batteries.
Do you have a roadside assistance plan like Coachnet or Good Sam's? If so, then they will normally cover jump starts. If the batteries were dead and then they froze, they may not be able to be saved.
Even if you have shore power, your interior lights are 12 volt and will require battery power to operate. When you say you could not get any power at all inside the coach did you try anything that was not 12 volt powered, like plugging something into one of the AC outlets?