Sorry for a longer answer, but I hope it may be helpful. That said, I must be the crazy one here because I don't do any of this with plastic bags/boxes/bins/anti-moisture packs. For clarity's sake, I will only be referring to the TBLeague Seamless bodies as that is what I own. I also live in the midwest USA, and if you have ever lived there you know how absolutely pointless it is to guess how the seasons will go, and thus the temp and humidity.
So what I do is I just let them stand on display. I have two figures in open-air dioramas (one of which I am very, very protective of), the rest are on shelves and a table. Sunlight does come into the room, but it is more natural light than it is "direct and blinding." I have a protective shield in place for that to protect what is in the path of the harsh light. Avoid direct sunlight if at all possible.
I do, however, routinely perform "maintenance" on them:
- First is setting a baseline. A few months back I took every single one of them, stripped them down, and re-applied baby powder to the entirety of their bodies, then redressed them. That way I know they are all as protected as possible in that regard.
- Second is the "touch test." This is meant to be a spot check, where I will gently run my finger along whatever happens to be the most exposed part of the body to see if it has turned tacky. Tackiness tells me that the humidity has nullified some of my protective work. Smoothness tells me that everything is likely fine. Fully clothed figures I do not worry about as the clothing protects them as well (especially when combined with the powder).
If I feel tackiness on the most exposed area, then I check others and respond accordingly with a soft brush and a bit of baby powder. Any powder on clothes is dealt with by an air duster. This process has protected all the figures I own for about 2.5 years now. No torn arm-pits, crotches, or other areas.
Granted, I have done similar damage from accidents while working with them, but not from them just hanging out in the open air.
Any "touch up" is a 10-15 minute process that I likely won't have to do again for another month or two.
- Finally, about every 5-6 months I do the full strip-down of them and reapply the baby powder. Again, so far so good. Probably about an hour or so process, but I also don't have as many figures as some of the others do.
Another thing to keep in mind is the pose of the figure, especially if a seamless body like TBLeague. A natural pose will likely work best in keeping things alive and well, but you can still get away with longer periods of more dramatic posing. Just be aware of it and change it often.
As for display case kinda things, I do like IKEA shelving and enclosed displays. Decently affordable and decent quality, they have treated me well.
Hope this is helpful!