My mechanic uses discarded scooter tubes. He cuts the inner strip in one piece, remove the valve, and uses it as a rim strip.
I personally feel there is no difference between using duct tape or any other kind of rim. If you wash your wheels or ride in the rain, eventually water will go pass the spoke nipples. It will find a tight enclosure, provided by the pressurized inner tube against the rim. No matter what kind of strip you use; the space inside will be narrow and the water will go in and will never go out.
My advice? Paint the inside of the rim with zinc coat, rust preventer, and then use any strip you have at hand just to protect the tube from the spokes. You will never worry again about water going inside your wheels.