a lot is going to depend on your state's transport laws.
here in michigan to travel with a gun the following rules apply
https://www.michigan.gov/dnr/0,1607,7-153-10366_37141_37706-31579--,00.html
Originally Posted By: "Michigan DNR"At all times when carried in or on a motor vehicle, including snowmobiles:
*Rifles, shotguns, muzzleloading and other firearms must be unloaded in both barrel and magazine and enclosed in a case or carried in the trunk of a vehicle.
At all times, when carried in or on an off-road vehicle (ORV):
*Rifles, shotguns, muzzleloading and other firearms must be unloaded in both barrel and magazine and enclosed in a case or equipped with and made inoperative by a manufactured keylocked trigger-housing mechanism.
here the magazine unloaded rule does not apply to detachable magazines. the magwell (and chamber) just needs to be kept empty for the firearm to be considered unloaded. the loaded magazine can even be kept in the same case with the firearm as long as its outside the magwell. on permanent magazines (tube mags, non-removeable internal box magazines on bolt guns, etc) you have to unload them.
when i travel to and from hunting spots, its with a hard case on the back seat. i usually only secure the latches closest to me so i dont have to remove the case or reach all the way across the car to unlatch the muzzle end of the gun case. i either keep my magazine in my pocket or in the case with the gun.
if there's two of us we each have the muzzle facing the opposite side of the vehicle you're sitting on . that way you can pick the gun up by the buttstock and keep the muzzle pointed down and not sweep each other and only load the guns after they're removed from the car.
you're only allowed to shoot from a stationary motor vehicle/atv if you're disabled.
http://www.michigan.gov/dnr/0,4570,7-153-10366_41825_51140-37448--,00.html