Chief, you've been out west too long! The apostraphe (a mark (') used:
to indicate the omission of a letter or letters from a word or phrase (Ex.: o' for of, it's for it is) takes the place of the "ou" in "you all": ergo; "y'all' is the correct spelling. LOL Stan (Still in Georgia.)

PS: Have fun in Sin City, and look for any WTBS sites that might have strayed up from New Mexico.