Not sure about you particular unit....
On most Thor units there is a Trombettta relay that connects the chassis battery bank to the house bank while either plugged into shore power or while driving as long as voltage is >13.5VDC. The relay is VERY prone to failure. Not hard to troubleshoot if you know where it is on your unit. Cost ~$70 if out of warantee. Better units available aftermarket.
FWIW
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