I was at NTC in the Mojave Desert in 1986 and I came across an OP where soldiers had left behind some C-rats. They must have been left sitting there in the sun for a long time because we had switched over to MREs for at least a year. The cans were too hot to hold with bare hands, but I opened up the cracker tin and the crackers were fine
At the time, I was carrying a M1911A1 made by Singer
I'm aware that only six were actually accepted for issue and that of that limited number even fewer are publicly known to exist, so I'll take that with a grain of salt.
Polymers are a complex subject as some are longer lasting that others in extreme temperatures. For example, the intake manifolds, heater valves, power steering reservoirs and antifreeze overflow containers under the hood of the car. They are subject to working temperatures of 260 degrees for a daily working life from -20 to 120 going from parked to end of road trip descending the Sierra Nevada into the California valley.
On the other hand the owners of G Shocks are aware the exterior molded parts and straps can degrade in as little as five years needing replacements. Substances like DEET don't help at all as it's a solvent.
Engineers pick their polymers to deal with the working environment and to prevent long term issues. If a polymer gun subjected to heat is bothersome, then an alloy framed gun with stainless slide and appropriated surface treatments can easily meet the task.
Heat isn't the real problem at all. It's humidity and swinging temperatures which could allow a cold gun to condense water on it from warm wet air. Same as a glass of tea when mowing the lawn, guns can and will do that. Cased, they trap the moisture so a recurring pattern in the spring and fall will cycle cause rust to get a foothold.
Then there is the issue of theft, and it's likely to become a bigger issue for the anti gunners in the future. It is being tracked and has gone on the upswing - people storing their gun in a parked car are noticeable, and there is more targeting of cars because of it.
There is also the added layer of difficulty with retrieving the gun and being familiar with its use when it's never taken out and practiced with. Too many sit inaccessible to the driver as if they will have all the time they need to stop the car, get out, go around to the back, retrieve the gun, etc. Anyone who has studied traffic light carjacking will easily see that you aren't going to be presented with that opportunity.
Far too many of the situations we could need a firearm require it be on you to respond. I see the "car gun" issue as a bandaid, a security blanket for those who won't carry. It's like a gun in the bedroom when you need it because you shouldn't have opened the front door - the #1 method intruders use to gain entrance. The gun is nowhere near where you need it.
Given the number of guns I have seen in pawn or gun store racks which are a mass of rust specks from car or truck carry, no, I don't see carbon steel being proof against it. Considering the number of vehicle break ins reported as the source of stolen guns, I wont go there. And not having it at hand when most of the likely scenarios seem to require it is the final straw.
If you think you need a car or trunk gun then you do understand the increased risk and are responding to that concern - however the solution isn't presenting good positive benefits to address them. A gun hidden away out of reach simply isn't a gun at all when you need it. Your ink pen in your pocket is a more accessible weapon and arguably better at the close contact ranges implied. Whatever else you encounter, simply mashing on the gas can solve.
I'm not suggesting ranchers or other rural inhabitants shouldn't have a truck gun, however, many of the negatives involved aren't in operation - higher density populations are the key issue, and they are the ones who present the dangers and also ransack vehicles. If you live around people in a cluster of inhabitants more closely packed than one per quarter mile - you aren't out in the country. It's suburbia and it's not as pretty as we'd like to think.
It's not the heat, humidity, polymer or ability to remain stored over a long period of time, its a people issue, and misapplying solutions to prevent being uncomfortable about carry doesn't fix the problem.
