My problem with 80s and 100s is weight and bulk. I have various physical issues that make that size tank problematic for me. For club dives, vacation etc. should be able to get dive buddy or whomever to help out if needed, but going back and forth from my car to the pool I need to keep the total carry under around 30lbs.If you are making multiple short dives, using a couple of bigger tanks on a series of dives makes more sense. If you are making dives to ten feet for ten minutes, just use an AL80 four times rather than a 5L pony once. a 30L tank won't fill a 5L cylinder six times. I think you are making the problem more complicated and expensive than necessary. Buy bunch of AL80s, use them on multiple dives and then drag them to the shop when they are empty. You could buy a half dozen used for the cost of a banked tank. And they would be much easier to transport.
I can look into renting a locker but I'm not sure the pool would want a tank of compressed air sitting in a locker all the time.
I guess I can also look into wheeled luggage although I'm guessing it will be hard or impossible to find something wheeled that is designed to get wet and dry out all the time.