I had a Dakota pickup built during that same era that would kick that alarm/code frequently.

It was usually a split/cracked rubber hose under the car. There are a bunch of them running the length of the car to and from the gas tank, charcoal canister, purge solenoid, etc.

They could be a pain to locate--I didn't have a smoke machine.

Seemed to me there was an issue with the hoses they were using at that time--very poor quality and always cracking.