Winnebagos in that era should have "heated" tanks but they are not heated by electric pads. They are heated by the ductwork that circulates the heat through the basement compartments. This is done by the LP furnace when it is keeping the living area heated.
If you read through the 7-year old thread in the link below (it's on an auxiliary forum --spin off-- of iRV2 so should be acceptable to link ...and it probably originated here on this forum), it will help explain the process. Some of the participants in that forum are still participants on this forum currently.
In fact, I think or hope the OP in that thread, Scott, may even chime in here.
Where's "Proof" that my tanks are heated?