Mal Drop,
your solution was identical to my proposal except that I intended that we slung slack chains across the a/c for them to hold on to. Of course with a really full load they were so packed in that any movement was rendered impossible and therefore restraint was not needed. The weights were always a considered guesstimate. In your casaevac 'experiment' did you have the full book casevac fit of 70 stretchers plus two attendants ?
As you rightly say humanitarian evacs usually meant much lighter pax without the troops very heavy kit.