I believe that the lounge closes at 10 PM, might be 9 PM if the LSL boards on time, the station itself closes at midnight. And they lock it up tight too!

As for storing your bag, since you're in a sleeper you are entitled to use the lounge and therefore can store your bag in the special room. You'll have to show your ticket stub, so don't lose it. Confirm what time they close when you check into the lounge what time they actually close, and then I'd still recommend getting there at least a 1/2 hour before closing to reclaim your bag(s).

And I can't imagine that the tip to the Redcap manning the room could be more expensive than the lockers out in the main waiting room (south side) and also in the baggage claim room. Those lockers are pricey!