98 Caravan SE - A/C - vents smell really bad! HELP...

I brought my car used. The previous owner had a golden retriever. Although
I cleaned and washed the entire interior. The car's a/c & vents when
turned on smell like a wet dirty dog. This is especially bad after it
rains.... I am ready to get rid of this car because it can't take the
smell anymore. In the summer when the A/C is crucial, it is unbearable!..
My brother also owned a caravan and he too experienced the same problem.
Has anyone else had this experience? Is there some sort of hidden air
filter that I can change? Or should I start saving for a new car?