Hi,
If you live in a "Shall Issue" state for CCW permits, get one of these first.
Also, research the exact laws in your state, and all neighboring states you may travel in to see how it is legal to transport firearms in their states.
Each state can be different, and ignorance of their laws is not an acceptable excuse, nor should it be.
The CCW permit would allow you to carry the weapon concealed within your vehicle. I can't see how a trunk gun could generally benefit you at all, for if you had time to retrieve and load it, and then used it, a court might rule against you that you also had time to run away . . . and didn't so you could kill someone.
Around my state of Georgia, we have reciprocacy laws in effect with Florida, Georgia and Alabama, the three states that border us. Because of this, I can carry in these states too . . . as long as I follow their specific differences of their laws properly.
I don't know where you live, but check on getting a CCW. Many states offer/require training and firearms and situations before you can get your license. This would also benefit you greatly as a new gun owner!
T.
PS: Right now? I'd probably recommend a revolver. They are very simple to use, very safe and utterly reliable. HOWEVER, many states require a non-CCW holder must have the gun UNLOADED, and that the ammunition must be somewhere else in the vehicle where it is not easily accessed.
Hope this helps!
T.