Slightly off at a tangent, but any theories about why build a barrow other than for funereal reasons? A cham bered long barrow has lots of possible uses I suppose, a cairn might be a boundary marker (but still quite a lot of effort to go to).

But are there examples of earthen barrows (long or round) which are known to have never contained any remains, even cremation? I guess it would have to a very intact barrow, in soil that was not damaging to bone.