My thoughts about good guitars in humid environments are that short term hi humidity is not the problem, its long periods of very high humidity (above 60%) and then a change to low ( <35% ). I keep my Collings guitar in a Calton hardcase with a dehumidifier in the string compartment of case. You can buy these dehumidifiers at gun shops or Brownells online. They are the size of cigarette pack, you recharge them so to speak by putting them in an oven at 300 degrees F. for 3 hours. They keep my guitar at 45-55 % humidity in the case for 3 or 4 weeks even when humidity outside is much higher. The key is an airtight case like the Calton, or if using a lesser case, get a case cover.
I think exposure to direct sunlight ( hi temperature ) is much more concern than short term exposure to hi humidity. I do agree that a cheap used guitar is the safe way to go. I like 80s-90s Washburns, all solid wood, find em on ebone or Craiglist for couple hundred or so for a D-35.