There isn't any place where water touches the wood, even when parking a wet vehicle inside after a rain. We'll see how it holds up this winter!
Doesn't have to be direct contact.
House across the street was completely rebuilt. they fancied up the front porch with nice handrails and two square, tapered pillars, both of which were trimmed out with that "white wood". All well under the roofline, but facing west - right into the weather.
Less than two years later there was a workman over there ripping it all out and I walked over and asked him what was going on. The "white wood" had been tacked onto the "inner frame" (such as it was) and then caulked and painted. Exterior appeared to be okay, until you pushed your finger against it - you could push hole through it with a finger.
Same exact thing happened on the new house that ex-wife's son bought out in Fife.
The problem, as I understand it, is that if it is used - even indoors - with ANY possibility of there being moisture present - you need to have some air circulation behind it.
In your case, I think the only areas I'd be concerned about would be those two very short sections of wall on either side of the garage door entrance and that center section below the fire extinguisher.
That said:
My sister is still waiting for me to go over and trim out the doors in her garage with that stuff, but she's got so much **** piled up everywhere there's no way to get to the areas that need to be finished. But those doors are on an inside wall - not much concern there.
YMMV
