P38 evap charcoal canister

Hi I got a 1999 Thor p38 (row spec) which lately petrol smells comes out of it while it’s parked mostly in sunny days cause a problem in the evap system. I’ve noticed today that I got a pipe going from the canister to the engine bay next to the expansion tank and when I asked few people about what it connects to all said that comes on nas spec only. What parts are different between the row spec evap and nas spec evap? And could I just put nas evap on it ? Or return it to how it was or delete evap and put a simple breather ?