Code P0455, ????

I have a (OBDII) engine code p0455, which states a GROSS evap leak. Was told this is normally a defective or loose gas cap, but replaced it.
The car runs well, code comes and gos...any ideas what it could be?
I am in the process of inspecting the EVAP canister behind the passenger wheel. Thanks everyone!

I would check the rubber hoses for cracks going to the evap canister.