I don't wash either of mine.
One doesn't have enough paint on it to warrant washing.
The other one is kept inside, and only gets detailed with a spray on/wipe off product using micro-fiber towels. If it gets dirt on it to the extent that I don't like the idea of wiping it with micro-fiber cloth, I will rinse it off with water, then detail it with the spray on/wipe off product.

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission