He was 64, so he wouldn’t have drawn many second looks in Vegas.
He probably used gun cases that would not draw attention to himself. Squared and not ‘gun shaped’.
He probably made more than one trip to the car to get them all up to his room. so again, no attention drawn.
He probably had them pre loaded, so he would not be lugging a case of ammo.
He most likely used the freight elevator and made sure no staff was on it.
He could have done all these things...............
He could have put them in guitar cases for all we know. It was a music festival right?
There are cameras EVERYWHERE in a casino. But the focus of a casino's security is to make sure that nobody cheats the casino out of a dime.
I've stayed in Las Vegas casino-hotels. For those of us too cheap to tip the staff, they supply large roll around carts to carry one's luggage up to their room. A customer could load a couple of steamer trunks on one which would hold all the supplies the shooter needed. It wouldn't raise an eyebrow.
The shooter could even have made use of the maid service by locking the trunks when he was out of the room. There were virtually no impediments to the shooter carrying out his plan and he would have been confident of that being true ahead of time.