Nice box, but aren't you going to need a flat pattern? That would mean you need to rip and bend reliefs. When I used to make boxes like this I would weld and grind corners to see them as spherical. Maybe I am missing what you are trying to convey.
There have been posts in here asking if it can be done. We have some sheetmetal parts whose corners after forming are spherical. I have accomplished spherical corners in the past by utilizing surface>advanced>boundaries, but cannot get it to work all the time. Yes, cuts and rips have not been done yet. The sample was just to show it can be done.