I only seal the bottom seam.
The 15 inch is good once you start stacking them because you can stack 3 or 4 without being crazy tall..... Depending on what the first one is on and how tall you are. My 3 are on a regular height table so they're pretty tall, but I'm tall enough to see in the high one and clean fine. But my wife would need a stool. 24 inch get yeah real quick when stacked.
I leave the keys in my locks but it's just my wife and I so I don't have anybody else to worry about.