[67cobain94]

I can't see a gas cap fixing it for only a few months at a time. Caravans are notorius for the Leak Detection Pumps going bad and cracked hoses. Remove the air cleaner box with one 10mm bolt and pull up to release the grommet. Follow the 2 lines off of the purge solenoid and see if it is cracked after the 90 degree bend or at the service port. If it's good there you need to look at the hoses from the Leak Detection Pump (NVLD solenoid) to the canister. If that's not it, you need to have it checked out for a LDP, a tank or a purge solenoid.