in suitcases. A high roller traveling heavy in Vegas with a bunch of suitcases wouldn't get a second look. He leaves them in the suitcases, so as not to be seen by maids, until the day of the shooting and then puts a "do not disturb" sign on his door and begins setting up his lair.
I don’t even understand why this is a prominent question. Hotels don’t monitor everyone going to and fro throughout the day, especially if they are a regular there. Obviously he hid them in duffel bags, suitcases, maybe even golf club bags and casually brought them up to his room a little at a time.