This is a common problem. The fix is to seal around where the A/C box drains out the water from condensation from the evaporator.
You have to smear silicone sealant around the area where the drain tube comes out into the engine (the fire wall it is called). It takes quite a bit of silicone to do this as the area is square around the tube and there is a rubber gasket between the A/C box and the firewall.
The key is to seal the area on the bottom as water drips from the tube it follows the tube back and leaks between the foam seal and the A/C box and runs into the passenger side floor and soaks the carpet.
There is also a 90 degree rubber trunk thing that you buy at the dealership that will slip over the drain tube to direct the water down the trunk and on to the ground so it never gets the chance to drain back along the firewall into the van interior.
2002 Chrysler T&C bought new end of 2001.
3.8 L 108,000 avg. fuel eco. 22.4
2009 Pontiac G8 GT fuel economy not determined yet, currently 22 mpg