The ammo would have only been 2 green metal tins if he had 2k rounds. The weapons he could have broken down and brought them up a couple of a time in a case or luggage.
Some riffle cases do not look like riffle cases.
It would be easy to bring them into the hotel and up to the 32nd floor room in a golf bag. Obviously the hotel lacked security checkpoints with metal detectors.
At some point I expect a class-action civil suit against the Mandalay Bay Hotel & Casino for lack of security that allowed the guns to be brought into the hotel. In this case such a suit might even bankrupt the hotel.
Another class-action civil suit against the estate of the shooter.