Use a small bilge blower, or compressed air--something explosion proof. A SCUBA bottle regulated down to half a pound would do nicely. I'll be doing something very similar on my new one.
I did not come up with this but my sealed battery container has two small hose connections that I can open and hook up a small aquarium compressor on one and the exhaust hose on the other. That way I do not have to open the lid while charging which in my sub is a big pain.