Describe how the heat and humidity hits them like a warm slap in the face as they teleport. How they all start sweating immediately in clothes designed for a temperate environment, and how the Paladin's gambeson and clothes become soaked and heavy from his own sweat.
Mention how people in positions where you would expect heavy armour such as guards or knights are stripped down to tunics and tabards.
Perhaps we misunderstand each other. Unless there's a mechanical drawback for keeping the armor, on, it will stay on. And if there is, players will want to know how to get rid of it, so the armor can stay on.
Furthermore, players expect NPCs to think the same way. Therefore, just reducing it to atmosphere and color doesn't cut it. There needs to be a mechanical reason why NPCs don't use armor while PCs do.
The most straightforward solution is to make the magic needed to keep using armor difficult enough to keep it out of reach of everyone but the most dedicated characters, such as the player characters. Difficult meaning either "expensive" or "dangerous" or simply high enough level, which it all boils down to.
Check the section on the merchant princes and markets. ISTR 1st and 2nd- level scrolls and potions are for sale by one of the princes.
I will have to do that.
Though if they're anything like the DMG's prices I'm not holding my breath. Usually, they're much too high for consumables (like scrolls), but in this particular case, I expect the price to be too low - if Endure Elements would remain a 1st level spell, that would make a Common scroll, costing (as a consumable) half of 50-100 gp.
In contrast, Sane Magic Prices (a document I trust much more) puts the price of a 1st level spell scroll at 60 gp.
This may sound rather similar, but as soon as we leave level 1, all similarities end.
Anyway, so a case of thirty Endure Elements scrolls would be roughly 50x30=1500 gp. That's
per month, and I'm led to believe Chult expeditions last longer than that?
Is this about right? Is this what ToA ends up at? Is this what you would consider useful and appropriate?