The Martin HPL models are a decent choice for weather resistance, and some of them sound decent too. They bristle at hearing HPL referred to as Formica but that is basically what it is. HPL is quite resistant to environmental changes like humidity and temperature, but it is not invincible. Martin models mostly have 1-11/16" wide necks. (I did look at the specs on those web pages, and these particular models have the wider necks. Interesting). I also like the laminated Stratabond necks. This is the equivalent of glue-lam beams in buildings, stronger and more stable than plain lumber.
The ultimate all-weather guitar would be carbon fiber -- Rainsong, Emerald, Composite Acoustics, etc. But they will be considerably more expensive than the Martin HPL models. As with any tool, it depends on what you intend to do with it.
