About two years ago, after one particularly nice but salty winter, I’ve found a very corroded valve hole in one of my rims. Sticking a nickel-plated brass valve in a hollow aluminium rim and pickling it for month creates a perfect example for galvanic corrosion.
Since then, I was wrapping some tape around the valve stem and used two rubber O-rings to electrically isolate the aluminium rim from the nickel-plated valve stem to see if that prevents corrosion of my rims in the future.
One O-ring goes inside between rim and tube, the other O-ring on the outside between rim and nut.
It really works. No nasty corroded valve holes since then.