Been there, lived that. My air consumption has improved somewhat but I have a higher basal metabolic rate than most people, due to muscle mass, and I'm always going to use more air.
Here's what I do:
- For local dives where I can bring my own cylinders, I typically dive a single HP120. That gives me slightly more run time than most people with AL80s.
- On local dives where that isn't enough air or where I'll be diving solo at depths greater than about 25 feet, I dive a twinset. I have one pair of LP72 twins, and two pairs of HP100 twins, and I have the parts to make up an HP120 twinset from my fleet of HP120 singles.
- While traveling I seek out operators who offer larger cylinders. For example, in Cozumel I use Aldora, who offer HP120s, and in the keys Conch republic offers HP100s. Most operators have at least something larger than an AL80 they will let you use if you ask, but too often it's an AL100 that is short filled to 90 cf, and that's not enough for me to keep up with most divers.
To be clear, when I'm speaking of a twinset, I'm talking about manifolded, banded doubles, that attach to the BC with two bolts.
My BC will allow me to dive independent doubles, which can be mounted ad hoc using cam bands. I've done this experimentally. Since there is no manifold, you have to switch back and forth between regulators, and have two SPGs. I might try it if I want to make a long dive in some place where AL80s are the only thing available.
While I have not asked, it is my perception that few dive boats will permit doubles unless you are on a trip that mainly caters to technical divers, and have a technical certification of some kind. They complicate cylinder handling and tend to lead to longer dives that complicate scheduling.
I dive a DSS backplate and wing. I have separate wings for singles and doubles. I believe this is the most common arrangement for people who dive twins.