IMO the charcoal canister is only to deal with fumes from the tank, and the only time you're going to get any venting from the tank is with a significant change in ambient temperature, like maybe having the car outside in the cold, taking it to the gas station and topping off the tank and then moving it into a warm garage where the fuel expands and vaporizes a bit. Most of the garage fumes problems are leaks, like the residual fuel pressure in the fuel rails passing leaky injectors, a blown diaphragm in a fuel pressure regulator, fuel boiling out of the carb bowls, etc.

I wouldn't start chasing finding/making a charcoal canister until you know that it's just tank fumes. Use your nose to hunt for the strongest odor around your engine.