1) acrylic tubes do not fracture because the disk + o'ring fits very tight, that's no good, but is not the reason. The tubes fractures because it happend, is a characteristic of extruded plexiglas, the manufacturer told me that, even before I bought the tubes, this material can fracture by being in contact with many liquids, and it seems that our e-liquids are within that group, even if nothing is doing pressure over the acrylic. The acrylic tubes works great but there are not for ever, because of that we must think in spare tubes.
Also, they may crack if you have nicked the edge while cutting, have done a poor job or used the wrong tool, or too much pressure to cut it and produced hairline invisible cracks that make a great start for a bigger one. To help prevent cracking due to these reasons you can flame polish the edges. It must be flame polished, mechanical polishing will do nothing to prevent cracking. It takes practice to get a good flame polished edge. Cast acrylic can crack too, but usually due to one of the above reasons. The stresses induced in extruded material when extruded give it an inherent tendency to do so, even when all precautions are taken.
Turbo, acrylic is by far the best transparent material for this purpose. Well, that's readily available to us for a reasonable cost. there are many engineering plastics that would fit the bill, but they are either hard to get, or very prohibitively expensive. If you wanted an opaque tank, then there are better options. There are some really slick, machinable, transparent glass/plastic/ceramic compounds that are quite tough as well as elastic enough that would be ideal, but your talking an $1800 tank tube.