I recently completed building a .300 BLK AR pistol (8" bbl.), with the intent of using it for home defense and to toss into the SUV for travel. I did a little research online and confirmed that registered/approved suppressors are legal in 42 of the 50 states (assuming we don't make Canada our 51st state!), and that no ATF notification of travel is required whether driving or flying. It was suggested to travel with a copy of the ATF approval form just in case some well meaning LEO decides to do a search. Also, since a suppressor is considered a "firearm", it should be properly secured during travel. However, I want to have quick access to my pistol should the need arise (God forbid!), so it will be zipper cased and sitting in the back seat of the SUV. I try to never leave a firearm unattended in my vehicle, so I may add a lockable box with cable lock to my packing list.