Eh, even with a carbon fiber neck I would still advise against this. For most of us who play with not-so-high profile artists, anyway
The resins that are used to bind the carbon fibers together do soften at elevated temperatures (this is called the "glass transition" temperature, referred to as "tg" in the technical specifications of the resin). Some resins higher than others; some get well into the range of 400-500 degrees fahrenheit, but some as low as 130. If there was some reason important enough that you had no other option than to leave one of these basses in a hot trunk, I would at least check with the builder on the specs of the resin they use.
Of course, a high profile gig may be well worth the risk if you're working with an artist who sometimes gets an inspiration and you need to be available at a moments notice for songwriting/recording etc. The reward, whether artistic, financial, or both, may well exceed the value of a tool that can be replaced.
No disrespect to composite basses - I've got 3 Modulus basses. But if I had to leave a bass in a trunk here in Houston, I'd choose my old aluminum necked Kramer.
Excellent point about the resins used, and definitely something I wouldn't ever think to ask! But, I'm not in the habit of keeping a bass in my vehicle if I'm not there with it either.
Dang, Houston?!?! Yeah, you probably know a thing or two about heat and humidity.
