I think you should be fine with just your rear view mirror. I would definitely be cautious about where I would park my car with everything opened some parts of DC can be scary. If you absolutely must drive around DC with the doors off, I would not leave anything in your car, and, leave it all unlocked. The last thing you want is some hood rats busting your locks on your glove box to steal something worth $10.
P.S. Sorry for a late reply.