If the HVAC (heater) housing is not properly sealed at the bulkhead (firewall), water can leak into the passenger compartment. Foam sealant should be used to seal any gaps and the evaporator drain tube can be modified to prevent further water entry.Google+
Car Problem Reports
Dodge Dakota Water Leak Due to HVAC Case Not Sealed at Bulkhead
Dodge Dakota Problem
Average Mileage: 106,037 mi (55,000 mi - 150,000 mi)
Visitor, 2003 Dodge Dakota, 101,000 mi
Passenger side floor soaked.
Visitor, 1996 Dodge Dakota, 150,000 mi
sounds like the problem i have. Took it to a shop, had them replace heater core hoses, clamps, and heater core. 3 months later, it is leaking again. Also, they could not get my defrost to function properly and was issued a refund.
wet passenger floorboard
problem started at about 50,000. dealership wanted $700 to repair the seal.