Here is how looks the 32k (LOD 0) rock.
To achieve this result that fast -by that I mean in less than 1 week of total rage, full annoyance and bugged bugs (3dsmax 2012 unwrapper can be very erratic)- I bought a 3dsmax plugin to help me to do the unwrapping, faster & better than I would do myself. It's called Unwrella (& UV-Packer ; it was a bundle).
Quite expensive (took me a long time to decide ^^; ) but the result is here : I was able to unwrap ALL the LODs in an hour (after messing a bit with the options).
Now I'm on the texturing/projection part.
On the image you can see the 32k (tris) LOD and how it looks if I duplicate it a few times to hide the bottom (hollow) part.
I might work on it again to close the bottom ; making a cluster version, but for now I'll just finish the rock alone. =)