This may or may not help, but it's well meant so here goes.
I had a similar problem with a '95 Escort, it was resolved by poking clear the drain holes on the opposite side to where the battery is. It's not easy explain but it's like a disused battery shelf for L/H drive cars, and there are a number of holes with a channel which gets corroded, fills with a small puddle and drips into the heater unit and soaks the carpet.
Get a metre or so of 2 or 3mm wire and poke them clear till the wire appears underneath, our cars are rather different but the problem seems the same so I believe it may resolve it.