The minimum standard that you are able to transport under is the federal FOPA standards specified in 18 USC § 926A - Interstate transportation of firearms
18 USC § 926A: Notwithstanding any other provision of any law or any rule or regulation of a State or any political subdivision thereof, any person who is not otherwise prohibited by this chapter from transporting, shipping, or receiving a firearm shall be entitled to transport a firearm for any lawful purpose from any place where he may lawfully possess and carry such firearm to any other place where he may lawfully possess and carry such firearm if, during such transportation the firearm is unloaded, and neither the firearm nor any ammunition being transported is readily accessible or is directly accessible from the passenger compartment of such transporting vehicle: Provided, That in the case of a vehicle without a compartment separate from the driver’s compartment the firearm or ammunition shall be contained in a locked container other than the glove compartment or console.
Note the description above does not require the slide to be removed nor does it require the gun and ammo to be in separate cases. You do not need to lock it in a gun safe if it is a vehicle with a trunk, but if you are driving a van or SUV, it is required. Either way, driving through snakepits like MD, NJ, NY, or MA, having it locked in a case is a good safety measure. They cannot open locked cases without probable cause or your consent.
Never consent to a search. If they do not need your consent, they won't ask for it. If they are asking, then refuse. If they ask you if you have a firearm, you are not required to answer. However, if you do answer, do not lie.
Do not stay overnight in any of the intervening snakepit states, and minimize stops.
For additional guidance, the NRA-ILA website is a huge resource -- and has better credibility than most internet keyboard commandos. Try the following links:http://www.nraila.org/gun-laws.aspxNRA-ILA Guide To The Interstate Transportation Of Firearmshttp://www.nraila.org/gun-laws.aspx#profilesTab
Now, when I say "minimum standard", some states are considerably more lenient in what they allow. If the state has more expansive rights, then those standards apply in those states. The NRA links above give the laws for any state you wish to research.