The brochure for your coach indicates it has an LP water heater (i.e. no electric heating element, only gas with an electronic ignition). It should be sufficient to turn off the water heater using the WATER HEATER switch at your monitor panel.
The 12V fuse labelled 'Tank Heater' looks like it's actually for holding tank heater(s), not the water heater.
2005 Winnebago Vectra 36RD