For what you've described the freezer ziplock bag should work fine.
I also bought one of the Aquapac PDA Classic Plus Cases (360) and the Cybook fits in it without the cover. I wanted to be able to take it in a boat so I could read while fishing. You can also use it in the rub a tub tub. The bag is blue so it's not as clear as a ziplock bag though.
http://www.modernoutpost.com/gear/de...aq_360_pda.php
It's funny if you sit around the house all day reading some people think you're lazy. If you sit in a boat all day reading then you're fishing.