My 40 DC has mid ship deck vents of 3" on each side of the boat.
The port is supposed to be for intake, the starboard for exhaust.
There are 3" hoses running from these deck vents to the mechanical area behind the bed at the transom that contains the fresh water tank, steering mechanicals/hydraulics, rudder shafts, etc.
We just removed the headboard panels to clean mold that had grown there.
The previous owner had installed the Nicro solar vents on each deck vent and I am pretty sure all they did was block the airflow.
Owner before that had installed 3" blower fans like used in the engine room but the fuses/fuse holders had long ago expired.
They are tapped off of the trim tab power with inline fuses. I got them wired up and running to test BUT
1) they are too loud
2) to use them would require installing switching/timers etc I don't mind that but since my gas tanks are under the bed in a connected space I assume I need to ignition protect all wiring.

Anyone know if these passive systems work well enough? Anyone know what parts were included with the original deck vents and how the hoses are meant to be positioned?
Any suggestions on blower fan setups? I definitely do not need 2 fans, just an exhaust.
95% of the time I would use a blower like this at shore power so I could use an AC blower, but then I am also not sure what is required for ignition protection etc since this is venting the gas tank space.
I thought of removing the intake blower and opening up the 3" hose/vent intake for better flow and then installing a fan in front of the 3" hose to send the air up and out the deck vent but in a way that also allowed passive air to move when the fan is not in use.
Thanks for any help!