I helped fix up an 02 Taurus that my sister in law bought for herself.
It had the trunk leak problem too.
I climbed in the closed trunk as my wife ran the water hose over the rear window/trunk area.
I found leaks in two sections, repaired them, and so far, no more leaks!
One section is a plastic clip that holds the rear window glass in position (when its installed?).
Its located on each corner under the black plastic lip that is attached to the bottom of the window glass.
This black wierd-looking clip is placed in two sealed holes to keep it in place.
With this car, the clip was partially broken off, allowing water to come through one of the holes into the trunk.
In this instance, since the rear window was firmly in place, I broke off the rest of the clip and siliconed those two holes. That solved leak #1.
Leak #2 was found where the rear bumper is clipped to the body using 5 push pins.
You can see these pins when you pop the trunk lid and look under the gasket that is located at the bottom of the trunk on the outside.
Water was coming in through these push pin areas.
I removed each pin, siliconed it, replaced and solved the problem.
Don't forget to check your front passenger floorboard too.
There was a leak there too, the padding was totally soaked and gross on this 02.
I tore out and threw away the padding, picked up the carpeting as well as I could, and ran a fan in there for 24 hours to dry it out.
I replaced the padding with some basement carpet padding I had extra and put it back together.
I siliconed around the air conditioning drain located on the firewall behind the engine and that solved the problem too!!
I hope this helps out with some of the trunk/floor leak issues for our other members.