A thought just occurred to me. OP wants something not prone to failure. Really, a squonker is adding extra failure points. A nice thing to have, perhaps, but not something to have to rely on in the toughest conditions.
A tube mech has a connector on top, and a switch at the bottom. Not much to fail, and some, like Kennedy, also offer replacement buttons/switches. I got an extra for my Vindicator. If the mod has a direct to battery connection, then heat sinks make cheap, and quickly replaceable, 510 connector. Most mechs that have 510 connectors have connectors that can be replaced by a $5 connector from Fasttech. A bit trickier to replace than a heat sink, though.
If I'm in an "Escape from NY" sort of situation, I would want a well made tube mech with me. But something lighter than a Vindicator. Maybe a 22mm that has extensions so you can use 18350/18500/18650. In most of these, you can also stack two 18350's. The classic is the Nemesis, but I don't like the button design.
I've bought like a couple of dozen or so clones in the past few months, as well as a few authentics. Many of the clones are good mechs (sometimes excellent) in their own right. One that really stands out is Tad's First Mod (also known as "First Mod"), by Footoon, a Korean company that makes top notch mods. I have the $10 clone, and it's one of the best built mods I own. Has a regular 510, mucho ventilation, and isn't too heavy. Stainless so polished it looks chrome plated. It even has a ring to lock your atty in place.
I have an authentic of another mod by Footoon, and the metalwork is stunning. Stainless is also much more durable than copper or brass. It just isn't as good of a conductor. Which I don't find to be a problem. The clone is $10, easily found on AliExpress. The authentics are out there, some at fire sale prices. $175 at Roadside Vapes, $50 at Delaware Vapor. A Google search will turn up a number of them at various prices.
Another one to consider is the CONSRVR mod by League of Scoundrels. I think Vaporrange still has some. For $40 it's a steal. The finish quality left something to be desired, but it's one solid mod. Solid copper or brass. It has the most ingenious 510 connector I've ever seen. It uses a copper ball to automatically adjust the 510 to your atty, but it's more solid and fixable than a floating pin (another weak point). Also means that battery adjustments and magnets are almost never needed. 18650 only. The bottom button/switch is very hefty, and uses a copper ball contact. It looks sort of weird, but the shape is really quite ergonomic. For $40 free shipping, it's a worthy addition to any apocalypse stash.
League of Scoundrels CONSVR Mechanical Mod Authentic