Unplug the rubber plugs in the spare tire compartment isn't really the solution. After all, the water still enter the trunk area, except you are draining it as it enter. The item in your trunk still get wet....
As for inspecting the venting assumbly, it should be simple. You should follow the same instruction in your user's manual for replacing the left rear brake light. Once the plastic panel is removed, you should see the venting assembly right under the brake light.
The vent is mounted on the body with two plastic tab on each side. The plastic tab tend to break off and cause of the vent assembly to seperate from the body and cause the water leak into the trunk area.
My 97 Camry used to have about 2 inch of water in the trunk after a heavy rain!!!
aSM.