What rights do we have against 'civil-forfeiture' when pulled over by the police?

Someone posted a story a while back about getting screwed over by the Pennsylvania police for his trailer while driving back from the Mopar Nats.

What can go wrong & what would be the best course of action when the police officer is asking you if you have any large sums of money in your car?

Say no to the sum of money then refuse a search(as is your right).