[Zanshin]

The Co2 is denser than air and YES, it poses a danger and risk in a sailboat. Not because CO2 is inherently dangerous, but because is displaces air and thus the oxygen required to breath.
CO2 is a by-product of fermentation, and even today one hears of vintners dying because they inadvertantly enter cellars during the wine season and either don't have their warning system (in the old days they would use a poor bird, just like the canaries in the coal mines) turned on. Even worse, occasionally rescuers succumb as well; not thinking of the speed with which unconsciousness can occur - one big breath can be enough to mess up your blood acidity and can cause unconsciousness.

But if you open up the ports and perhaps turn the fans to point to the bilges you should get enough movement to mix the relatively small amount of CO2 that sublimates.

p.s. A friend of mine had an incident years ago when his CO2 alarm system was faulty and he almost died, so I might be overly sensitive to the topic, so take my words with a grain of salt but realize that there is a potential danger.