@Schwob easiest way to do it is to backmount a single tank, and sidemount one. Easy as putting a loop bungee on the left side of the backplate.
It is possible and relatively easy to mount bottles with an independent doubles kit though those are relatively hard to find. You do have a wrong valve on the left bottle which makes valve drills weird and it is not IMO a solution for any sort of dives that require that sort of redundancy. Basically using it as a glorified pony bottle or gas extender
Thanks. All that is pretty much what I thought too, except I am not sure I yet understand why 1x BM AL80 + 1x SM AL80 would be easier than just 2x SM AL80.
I do think that the extra SM tank so would be more streamlined than the same tank slung like a pony w/o a bungee pulling the valve in. So I get that part, if that's what you meant.
For travel one sort of would have to decide ahead of time which kit to bring (SM or BP&W and a little HW to SM another tank and if bringing a pure SM kit, BM is not an easy option.
My experince is limited however to mostly BM (with slung AL40 mostly, sometimes AL80... or w/o if buddy diving) and I played a very little with BM doubles. But I recently also started SM to see what I think (just warm water so far and also learning wreck penetration in SM (both properly in a class). There definitely is a learning curve, but It felt pretty comfortable I'd say. Lots of improvement potential of course. But that just pretty much describes my diving in general, likely for eternity.. I see that in part as the fun part...
Anyway coming from there I guess I haven't yet scratched the differences that make so many say that BM doubles is easier than SM.
I do get that getting up a narrow ladder space with both SM tanks on if handing off one tank is not an option (sea state or boat rule or...) is hard. Outside of that?
So, not questioning what you or others say, just looking for the insight so I know what to, pre-emptively, look out for and to make good choices before stepping on the boat (Shore diving wise I also don't see the SM disadvantage yet). What is it really then that makes SM sometimes the less opportune choice and other options the better choice?