Thanks for the ideas. But, like you, my options are limited. Pool "kits" of any type simply are not available and would be prohibitively expensive to import. Shotcrete/gunite aren't an option and I'm trying to avoid "poured" concrete as it would have to be done using a one-bagger (mixer) and a continuous pour from floor to wall would be tough to do (planned size is 12x33x5 with a 10x10x1.5 T-stub), and I hate the thought of the formwork involved. The besser blocks are interesting but not available (from adbrimasonry) in Nicaragua. However, a surprising part of living in Nicaragua is the "can-do" (more like make-do) attitude of many. I came across the besser blocks before and asked a company that makes an excellent quality block if they could do a special run. They say they can and costs between changing the dies/molds and the saving in material is a wash.
I don't want to hijack your post with the details of my construction. Hopefully, time permitting, I'll get my post rolled out in the next 2-3 days (it will include "Latin Latitudes" in the title). Ferrocement is looking pretty viable as an option and it would be great to keep in touch as we move along (quite possibly a similar path).
Back to your project. I took a look at the Nicaraguan (Finca Zopilote) video you mentioned. In it they applied the mortar from both sides simultaneously (more or less) over what looked like a fairly thin "single layer" armature. The final result looked great. However, this was for a fairly small cistern. In several other videos and photos I've looked at, for small and large "containers" alike, a concern was raised, particularly if the armature was thick (or "two-sided", or double layered, with an space between the wire mesh layers), that there would be voids/air pockets in the center due to the thickness and being unable to compact the mortar sufficiently through the mesh to the center. I can't really tell from your photo what your armature looks like (in cross-section). Could you comment on how the mortar will be applied and if the above concern is an issue for your armature? Thanks.