The blower is sealed and is not in the battery box anyway. It's outside of the battery box where the generator is. It's a squirrel cage bilge blower, which are always sealed (at least the ones I've seen) due to being used in the bilge of a boat where gasoline fumes build up. The only part of the blower in contact with the battery area is the squirrel cage wheel, and the inside of the scroll in the housing. The motor is completely away from any battery fumes.
The reason the box is sealed is partially due to its location. The charger, inverter, and Vanner equalizer specifically state that they not be in the same compartment as the batteries. I might just use a cheap timer to turn the blower on every so often when the charger is receiving AC power. When the bus is moving, air will naturally circulate through the area. Thanks for the concern, though. One never knows what kooky idea somebody will come up with that could end up being dangerous.