We will be making an announcement this coming week on a new specification specifically for metal tube mods.
One thing it will almost certainly include is three (or more) milled slots in the body, to vent gas no matter what goes wrong. It's become clear that you need both gas vents and a blowout plug - but large slots would do both jobs, and are the easiest solution. Slots can be milled in any metal tube of any kind, and that basically fixes it.
It would also be nice to have a master on/off switch, and either an electronic fuse or collapsible spring fuse, as well. But it looks as if milled slots are the easiest to achieve in any tube mod. Of course, they have to be done on a mill, which many garage workshops don't have. Or, it costs $5 or something to have a machine shop do them.
This problem isn't going away soon, and as usual we have to increase the pressure on vendors, in order to fix it. Too many of them are still selling solid metal tube mods, along with two-battery configs, and even selling batteries with a C rating way too low for the duty. If you can go out and buy a solid tube mod that takes two batteries and the cells with it are under-rated, then you are pushing the envelope from Day 1.
OK for cheap risk takers maybe, not OK for people who just don't realise the risk they are taking. One day soon a mod maker will get sued for his house, car, and the clothes on his back. And when that day comes, I will be in court to give evidence against him - and be glad to do it. It's gone too far.
The only people who could actually fix this is a trade association. The main reason that vendors won't form a trade association is they don't like the idea of being told what to do. A lot of us think that day is way past and they need to wake up.