I have heard stories of entire engines sitting uncovered out in the rain. They dump the water out, put in some fresh plugs and fire it right up.
My teg sat with no front clip under a car cover without spark plugs for a while before I bought it. Dumbass thought the cover was waterproof but I had to dump oil in the cylinders and crack it with a breaker bar before it would rotate, seized solid. Oily watery mess shot out of the spark plug holes once I cranked it. It ran great for a few thousand boosted miles, compression wasn't perfect though.
Once I broke the pistons and tore it down I noticed there was a rust pitted ring around the cylinders where the pistons were sitting that didn't hone out.
I've heard those stories too, but water and time is evil to anything steel, maybe if the cylinders were protected and the crank case fills with water sure everything is coated with oil and mostly protected. But get it in certain areas and let it sit will fuck shit up.