I've only taken my Cybook on day hikes and I was very careful how I packed it. I haven't had a problem but for the hiking that you are describing my personal recommendation is to wait for a device with the Plasticlogic displays.
You could also consider a PDA or iPod Touch but I had the display of one of my PDA's break from the vibration of riding in a Go Kart. The displays aren't as large though and it's hard to twist them.
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