water keeps gathering in the trunk on the drivers side in the little pouch where the plastic liner sits. Even if the car sits…water collects. The car is in mint condition but the wate is causing rust on the dirver side 1/4 panel just behind the wheel well (below the fuel tank door). Is it a gasget seal on the rear lamps on the 1/4 panel
Have someone get in the trunk with a flashlight, close the lid, and hose down the area around the trunk with water to see if a leak can be located.
There is a body plug there.See if its not missing or deteriorated.They are available at your Toyota dealer.
Good ideas above. Another idea, a common place for rain water to enter the trunk is right above the tail light. Open the trunk, and you’ll see a sort of rubber gasket material there. Has it come loose?