I would not go sailing without a guitar. We bring one even on week long canoe camping trips. Garbage bag for rain.
A few years ago I bought an inexpensive but amazingly decent (used) guitar to bring on our tiny Victoria 18 for a week of camping on Moosehead Lake. No case, we needed every 1/4 inch of room! That cheap used guitar beat the socks off so called travel guitars that I've owned or tried.
I've since gone back to bringing a nice handmade with solid tone woods, no plywood. I want (and need) the better sound. Life is short.
I sail for enjoyment - not pay, and I play guitar for enjoyment. Really nice sounding guitars have a feeling to the sound that greatly increases my enjoyment. Some rare nylon string guitars have a good sound as well, with less tension than steel strings. They seem to react to temperature more than humidity. I call them "rubber" guitars, no offense I hope, and I have one I enjoy, I just can't get quite the snappy rhythm out of it as I can with steel strings. Excellent for noodling around on though.
My experience agrees with Bob Perry, it's lack of moisture that hurts. Here in Maine a heated house in the winter is much drier than even the desert, so I take precautions to keep up the humidity.
Back in the 70's I purchased (with help from a pro musician) a handmade solid wood guitar which has never been indoors since I got it. I kept it in a tipi, and now in my boathouse. Not even bitter cold (way below zero F.) has hurt it. BUT, there are no wild temperature swings like you get going in and out of heated buildings. Of course, I don't let the open fire shine on it, that cracked my sister's guitar with a big BANG! Don't let the sun shine on the case where you store it.
I find that when I buy a new guitar, it changes after a bit of outdoor experience, shifting somewhat. I've always worked on it myself, being too far from luthiers. Lowering or raising the nut or bridge, adjusting the torsion bar, just using my judgment of what needs to be done. Then once it settles down it remains stable, with a slight seasonal change. I have good hardshell cases for most of my guitars - all the good ones.
I use elixir strings, they really do last longer. And while my steel string guitars seem to stay in tune really well (especially the one that never comes inside) I still fine tune the strings at the start of each session, I want the harmonics accurate and true A 440 concert pitch.
I have not (yet) taken on the boat my best guitar, with the label signed by Chris Martin and autographed by Merle Haggard.
This summer someone nearby sat on his deck, leaned against the cabin, and played acoustic guitar while we were anchored out at one of the uninhabited Maine islands. Very nice, beat the heck out of people blasting tiresome radios.