Hi Dan,
This gas tank fume/pressure issue appears to be common and as JT mentioned has been discussed on the list recently . I have the same problem in my '95 EVC. The consensus seems to be that it is related to the charcoal canister / evap system. However, I haven't seen anyone post back with a clear fix for the problem. If you or anyone is able to solve the problem I would love to hear the solution! It's certainly a potential safety issue not to mention the fumes are extremely annoying especially with the driver side window down on a warm day.
Best,
August
'95 EVC?