There used to be an issue with the foam inserts in both metal and plastic boxes, emitting harmful gasses when the box gets hot. That's why case makers went to an inert foam insert some time ago, back in the 90's I believe. Back then, foam insert material was made specifically for equipment cases although even then I doubted its utility.
I've always felt that if I'm in a comfortable environment, my gear should be ok as well. While I've never really considered any toxic emissions from PVC or other plastic cases, I'm pretty sure the manufacturers have. Plastic cases are great for lightweight waterproof or at least resistant equip. containers. Personally, I like Rimowa and Zero Haliburton metal cases for cameras and Anvil wood-based equipment cases for all my lighting. I also like Domke and Kinesis bags (http://www.kgear.com) for breathability and all of which have refillable or reusable dessicant containers. In a pinch, I've also used charcoal briquettes wrapped in a layer of cheese cloth or something like it, placed inside cases and bags to absorb moisture when I didn't feel dessicant was enough.
Take it light ;>)