I can’t believe your Windsport does not have a BIRD, BIM or BCC. I think all Thor Class A’s have a means to charge all the batteries whether in engine, generator or shore power. Easy to check. Buy a cheap volt meter, turn in the generator or plug in and see if the voltage on the chassis battery changes to around 13.5v or more when you do. Sounds like your chassis battery is shot. The chassis battery is not a deep cycle and it cannot take very many deep discharges before it is toast. NAPA or any auto store will check it for you.
As to the coach batteries, have them checked at the same time. The way these coaches are designed, they will slowly discharge if the coach batteries are not knife switched too.
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