Zumo XT and extra protection on dirt bike

[FBF]

Hi, I have for many years ridden a dirt bike green laning and have during my time seen some pretty freaky accidents which could potentially spell disaster for a sat nav.
Up to now I have used a PDA in an otterbox and later cheap modded sat navs that were not waterproof but survived (mostly)
I also have a roadbike which ideally I would like to use the Zumo on too.

I am about to buy a Zumo XT because its basically a lot better than any of those but obviously a significany investment compared to the previous offerings.
So.... my questions are:- 1) is there a reasonably priced secondary case or buffer that works with the XT? Up to now all I have seen are shades and cases that are not particularly useful in that they are unpowered and not dedicated to the Zumo.

2) Can you buy a powered mount same as the original so I can swap it from bike to bike.