Yes, I did!
I took the floor mat out and left it, cleaned all around the boot (trunk if your american) and took out the rubber strips on the roof, cleaned out all the gunk and glued them back on.
One thing I noticed on mine was underneath there are some rubber bungs on the chassis. Mine had come loose. Once I had a tight seal it dried out and hasn't been wet since.
It might be worth trying all of these. I hear this problem is common on Celicas.