[twistedsymphony]

honestly you're battling against 3 elements
1. UV light (sunlight) - probably the most damaging of the 3, can fade the ink on the box and permanently de-value your collection.
-simply keeping this in a location where day light cannot hit the package is enough to protect them

2. extreme humidity - if you live in a really humid area long term exposure to highly humid air can change the properties of paper based packing materials, causing them to swell or become discolored. Extreme LACK of humidity can be just as damaging causing things to become brittle and crack.

3. dust/pollen - not really that serious since it can in most cases be easily cleaned off it is an eye sore if you have your collection on display. Also if you're handling your CEs often for the sake of cleaning off dust you're more likely to accidentally damage them in some way.

smoke etc. if you're a smoker or your collection is exposed to smoke or some other agent it can cause serious damage in terms of yellowing or the scent soaking into the package...
---

I just leave mine sitting out on a shelf, the only thing I'm really concerned about it protection from day light.

if you're interested in protecting a sealed game and still want to display it I would think shrink wrap is your best bet... they sell machines that can do it for you.... most CEs have such different size and shape boxes that you'd have a hard time finding some other kind of case that fit more than a couple specific CEs well. This will protect it from extreme humidity, dust and other air based harm. doing this and keeping it out of day light is probably the safest route.

a hard plastic case is kind of a bad idea IMO, first of all you'd be hard pressed to find a case that can adequately cover more than a few specific CE's, I found that rubbing/rattling around inside the case can be damaging in and of itself and it doesn't protect from humidity... really all it does it protect it from dust, but you'll still be dusting off the plastic case anyway.

a better alternative if you don't want to shrink wrap would be to simply use a glass front shelving unit... that will allow you to see your CE's, and access them and still protect them from dust... as long as humidity is managed in the room well and they're kept out of sunlight you wont have much to worry about.