Because the crankcase is ultimately vented to atmosphere, your crankcase environment will follow ambient temp and humidity, albeit with some delay. In cold climates with very low dew points, the inside of the engine is as bone dry as the air is.
Are you following a monthly exercise? If so, that exercise at no load will generate a small amount of crankcase moisture with blowby (very minor). But the oil won't get hot enough (no load running) to burn off the moisture, but usually the moisture isn't a problem.
The locations that tend to have the most problems are those with high ambient humidity and temperature cycles that go below the dewpoint. Think somewhere like Charleston SC or Atlanta GA.
Your engine is a big chunk of cast iron and cools and warms very slowly compared to ambient air. That means that after sunset the air temperature is always dropping faster than the engine temp, so there is no possibility of condensation.
But in the morning with dew on the ground, the air temperature is rising faster than engine temperature. That means the engine temp can sometimes fall below the dew point and you can have moisture condensing inside the engine. This is the primary risk for corrosion and acidity in standby gen sets.
A monthly exercise helps manage some of this, but because exercises are almost always done without load, the actual heat into the engine isn't very high.
So oil analysis becomes critical to assess whether your generator is seeing moisture issues at your location in your usage. In coastal areas where the air humidity can have salt in it, I've seen rust INSIDE the engine (on the cams) on generators that sat inactive for awhile. I probably don't need to tell you how bad rust on a precision ground hardened surface can be.
The easy button is a heating system that is configured to always keep the engine above dew point temperature. Large data centers and others with critical gen sets do this. They use large industrial V16s and the water jackets are at 120F or hotter all the time. The oil is warm too and ready to go at all times. This is because they have to have their gen sets up and online in under 10 seconds, so there's no time to prelube or warm the engine at all.
