I'm currently using the 3M backing that came on the cradle. So far, so good. That stuff is really adhesive.
I made sure the surface was totally clean and held the sticky part down for about a minute when I first applied it. I honestly don't know if I'll be able to take it off if I ever need to.
If it does come off, I'm sure you could get some double-sided 3M tape at OfficeMax or something that's just as strong.
