Here in california, the correct response is always No. If you say you do have a weapon in the vehicle, you will be sitting for about 1/2 of an hour minimum, while they run every single serial number, you may be handcuffed and sat at the side of the road. and from my experiance, the police typically do not treat your firearms with any respect whatsoever. I've had to lay them in the dirt, and I've been prevented from wiping them down with oil or cleaning them before putting them away in their cases etc.
If they are legally stored in the trunk and for whatever reason the police officer decides to search the vehicle and finds them then oh well, guess I forgot to take them out of the car last time I went hunting officer.
Its a bit different for a CCP, you actually have a legal obligation to reveal the fact that you are carying.
Just don't come off as an a-hole, don't plead the fifth, don't refuse to answer questions, you're just giving them probible cause to trash your car and ruin your night.
IANAL so take this with a grain of salt. It probably also depends on where you are. here behind the wire, the word gun translates into the officer trying to stick you with anything they can while you are now late and miserable with your car torn up.