Get three cloth gun cases.Put the guns in them before you get to the bank.Place them in a briefcase or laptop
Absolutely DO NOT put the guns in cloth bags! When you return, you stand a good chance of having three rust sculptures.
Go to your local Ace Hardware and get a spray can of LPS 3. (Have them order it from their warehouse if they don't have it locally.)
Spray each handgun liberally, and let them sit out for a few hours to allow the paralketone to "dry."
Place each handgun in a ziplock bag and squeeze as much air out before the final closure.
This is a tried and true method of very long term storage. I lived in south Florida for many years and long term stored all my guns this way. Never had any rust, ever.
Regarding a safe deposit box, I wouldn't worry about bank policy. What you put in there is your business, not theirs. That is absolutely the safest way to store those guns. Just carry them into the bank in a briefcase or lunch box or whatever you have. It's all private. Just like the military policy: "Don't ask, don't tell."
Look at it this way: Suppose you did put the guns in a locked vault and then put that vault in public storage. Somebody breaks in and just takes the vault, then opens it at their leisure when they get home.