The 22 did not have a gas-tank locker until O'Day re-tooled the deck mold for the 1977 model year (I think the forward hatch was also changed at this time, becoming a flush closing hatch, with the opening molded as part of the cabin top.).
It should be safe to leave the tank in the cockpit on the older boats, but I'd be sure that the tank is secured to avoid it moving around and it would be best to fit a cover of some type above the tank to keep the sun off it, reducing evaporation due to heat. As to whether to leave the vent open or closed, the tank manufacturers correctly tell you to close the vent when not using the engine, however....then pressure may build up in the tank swelling a plastic tank, possibly increasing chance of a leak through fittings. Metal tanks in good shape should be fine with vent shut. If the tank is an OMC/Bombardier tank, they all have a one-way vent, they only vent in, so theoretically fumes won't escape. They still tell you to close the vent on tanks that have vents, but we never closed the vent on the tank for our CAL 21 (stored in the cockpit footwell under a lid). Closing the vent should prevent moisture from condensation getting in to contaminate the fuel, unfortunately...the E-10 gas we use now is known for absorbing water more than the older blends.
I would not recommend storing any gas tank inside the boat (tank locker sealed off from rest of boat is OK) due to the risk of fumes leaking into bilge, and any fuel leaks also end up in bilge. Any compartment where portable fuel tanks are stowed must be ventilated, at least 15 sq inches of opening for each cubic foot of volume (a 3" dia. vent duct/hose meets that). A permanent tank is different since it is vented overboard itself.