For those of you installing or contemplating installing a "bilge blower" under the rear seat of your VDub to increase heater output, here's a trick way to turn the blower on/off...............
Rather then adding a separate on/off switch, mount a toggle switch under the rear seat that is
controlled by the movement of the heat distribution lever. (Its the left one between the seats.) When the lever is pulled up, the toggle switch powers the blower(s), when the lever is pushed down, the power is switched off.

Use a basic on/off toggle switch with a
metal lever, drill a hole in the lever so the stock cable can run through. Mount a single terminal cut from a plastic "European-Style" terminal strip on either side of the lever. When the cable moves, they hit the lever to turn the switch on or off.
Brackets are made from "shop scraps" as needed.
You can run the power wire to the fuse block to provide switched power when the key is on. To keep wiring to a minimum, you can connect to positive battery power available under the seat. You'll need to remember to turn the blower off when you shut off the car.
Glad to provide further details if needed.