Looking down the list and no responses on your question......so.... my 2013 ACE 30.1 was delivered to me new with the engine air box round cap removed from that port. I think you are correct that it is a drain port since there were many issues with air boxes filling with water and soaking the air filters on some coaches, as I recall. You would think though that a drain port would be positioned facing down not facing the front cowl. I have been running with this port open since Sept 2012 and have never had a problem in heavy rains etc. Maybe it also acts as an air intake supplement to the normal snorkel inlet air which faces the passenger side in my coach.
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