In Texas you must have it in the open or in a manufactured case.
Wow, lots of wrong info in this thread. I'm kind of shocked actually.
Texas has basically NO long gun laws (other than hunting laws around what can be used to hunt).
Concealed, open, loaded, unloaded, cased, not cased, burlap sack if you want.
Heck, strap it to the hood and that would be legal too.
I always find it funny when people ask for a cite of something that is LEGAL to do.
Texas Penal Code 46.02 - Unlawful Carrying of Weapons
Sec. 46.02. UNLAWFUL CARRYING WEAPONS. (a) A person commits an offense if the person intentionally, knowingly, or recklessly carries on or about his or her person a handgun, illegal knife, or club if the person is not:
(1) on the person's own premises or premises under the person's control; or
(2) inside of or directly en route to a motor vehicle that is owned by the person or under the person's control.
Penal Code 42.01 covers Disorderly Conduct, really the only other place firearms are mentioned:
(8) displays a firearm or other deadly weapon in a public place in a manner calculated to alarm;
Laws only make things illegal. So, if it's not mentioned, it's legal. Texas Penal Code ONLY addresses handguns as far as carrying, not a word about long guns.
ETA: Nothing in the hunting laws either:
http://www.tpwd.state.tx.us/publications/annual/hunt/means/