Dtc P0440

1999 GMC Sierra, 5.3 L. , 60K miles. Replaced melted plastic hose (~3/4") and vent solenoid but still getting P0440 code about every 2 weeks or so. Gas cap looks good. Another piece of plastic hose near tank appears to be distorted from heat or chemical but doesn't appear to have any holes in it. This is a tough one to diagnose as no leaks are visible. Can smoke test be run at home? Any ideas or help appreciated.