Adding a second evap canister will cause your VW Rabbit to fail the visual inspection portion of the smog check. We'd recommend dropping the fuel tank and inspecting the hoses/lines to and from the tank. Check the return line from the EVAP canister for pinching; or perhaps gunk build-up, not allowing vapor to return to the tank thus saturating the EVAP canister.
If your VW Rabbit is equipped with a Fuel Expansion Tank, inspect this component as well. The expansion tank accommodates the expansion and contraction of fuel in the tank due to temperature and pressure changes. A properly functioning expansion tank should vent fuel tank vapors to the charcoal canister as needed.
