Find the leak.
Determine if it is exhaust [Commodave} or fuel.
If , as mentioned it is raw fuel, you need to find it. Venting it won't stop the problem.
I had several leaks years ago. Was making me sick from fumes. There were several sources. Improperly sealed tank fittings for the fuel feed lines, crap hoses for the main tank fill lines and vent lines, diesel stove control valve leaking, engine leaking from a split fitting.
Some were simply a matter of looking and dealing with the resealing or replacements as needed. Some expense and work.
The engine was a lot tougher. I had to get down while the engine was running loaded and closely examine it. Traced it to a split feed fitting that leaked only when the engine ran, loaded. Heat from the engine would evaporate any liquid at idle or when shut down before I could get into place and of course I had no idea where to start the looking. Under the loaded run, HEARING PROTECTION, I could then see the fuel and trace it. As far as I could tell it never hit the bilge but evaporated
Get some of the Scot Blue paper shop towels. They show a distinct colour change if wetted. Wipe or wrap them around suspected areas.
A white towel will not show that change much so makes tracing much more difficult thus more likely to miss a source.
Wipe down or wrap those towels around any possible leak areas such as fuel pump, injection pump, fuel feed and return lines, diesel fired heaters/stoves, fuel tank fillers, vents and their associated hoses, fuel filters, fittings as they may not be tight or if a Fare copper fitting the sealing face has been damaged.
Check clamps too as hoses, as they age, often take a set [shrink] allowing weeps to occur.
I got them all , just took some time and effort. Now people come aboard and they do NOT detect the smell of diesel.
But ignoring them is not the way to go.
Fans may help temporarily but I would not modify the boat by cutting holes. Figure out another way to vent using ducting to an open but blocked window.
EXHAUST can often be spotted by a close examination of the exhaust system by CAREFULLY looking for any black spots from sooting. Could be a failing gasket, loose fasteners. Exhaust usually though does not have the distinct odour of raw fuel. However it will stink AND it will plug air filters in short order and clog aftercoolers which can cause other trouble.
Of course up to you. Happy hunting.
