I've taken different guitars all over the world, from the humid tropics to the north country, the neck was never a problem. They've been in dry airplane cabins, to the beach. to the rainforest to the desert .. Let's see ... the neck woods would've been ... plain unroasted maple, finished of course and mahogany, and again finished. Oh yeah ... sapale too. Yep ... no problems with those woods.
In terms of unfinished woods, why don't you pick a wood that comes from you're part of the world ... GA would be nice, another brazilian member here likes canary. I heard if you ask Warmoth they might even have brazilian ebony. You got lots of options.
And what's more stable?
Warmoth won't sell you a neck that's unstable. Probably living in the tropics and never taking your guitar anywhere would make the neck more stable ... if it's always hot and humid it's always going to be the same, right? Unless you use airconditioning.