tanya make sure its waterproof because it doesnt matter what you do if its raing its going to get damp and a lot of electronics only have to get near water and they die.
Could always park the bike in a garage while its raining supose.
Also due to the nature of the 6r if its in a tank bag it may have dificulty picking up satelights because you will be hanging all over the top of it and i am not sure how it will go, may still be okay i have only used a little garmin in my boat and it needed clear sky to work properly...may be diferent for a street map style one and it was 10 years ago.
go for weather proof at least and you should be able to power it up off the bike battery because you dont want to be mucking around with batteries.
If you find something you think may be ok try to google up a review before you buy it.
Could always follow the trail of breadcrumbs i left on the way back from the gp.
