Yeah. I see what you mean about the seams there.  That definitely looks like it could be a tricky effect to model.  I tried it myself just as a challenge the other day, and was not able to do it without overlapping the verts in those corners.  At least not with extrude or chamfer, but maybe there's other techniques that work better.

Just for kicks n giggles, I also gave it a shot in Blender, thinking maybe it had some algorithm in it's edge bevel that 3dsmax didn't, but once you push those edges inward, the same thing happens with the verts in those corners, so it's a universal modelling issue, not just a tool thing.  Great work overcoming that delimma here, however you managed to do it.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.