I have already built a small test cube for working out things like this, so I have been experimenting on that.
I found a company that sells machine feet and ball corners. The feet work well and even look okay, but at £5 for 12 I'd be looking at £200 worth of feet! Even buying in bulk from China, it looks like £100. Meanwhile, the ball corners looked surprisingly ugly, were slightly too small, and weren't really round enough to stop one cube piece damaging another.
|Prototype tyre-based corner|
The strips of each corner can be glued together with rubber cement. Once fabricated, the completed corners can be left unattached where necessary, to permit disassembly and final assembly on site.