Appears being more physical defensive is popular for Doubles Cressy. I'll keep those natures in mind while I prepare for tackling that moon duck although doing a Relaxed one is an interesting idea.Bold is by far the most common nature in VGC/Battle Spot doubles at the moment.
If you're going the VGC route with it I'd go Relaxed. Makes it a better TR setter and Relaxed plus 100 Def EV's allows it to live a CB Knock Off from Bisharp.
go relaxed, dont think anyone have done one yet :3