Depending on which model Winnebago you have the Transfer Switch may be integral with the Surge Suppressor like mine shown here in the top right corner of the pic.
There is no manual intervention for mine - it is automatic. I can't select what power source to run on. I can run the generator while on shore power, and I believe the transfer switch will switch to gen as a power source automatically, but I'm not sure which is priority on the transfer switch. Best bet would be to shut down shore power to avoid any surge to ACs or heat pumps running.
