After a few hours, my lumbar would be killing me. I use a 1" memory
foam (firm) between back and parachute but needed something more
beneath the lumbar area.
Just before my 9 hr. flight to GA, I forgot to rig something and had
the wife shove my canopy cover into a small sack and place behind my
lumbar before clipping into my parachute.
At first it seemed a little overboard but as it compress within 30
mins of flying, I had the most comfortable flight ever and not a pain
in the 9 hrs. That was in 08 and cover still gets shoved there
everytime I fly and still works.
That said, experiment and allow for compression into the comfort zone.
One thing to consider.....what will happen in a accident I have no
clue and I could be risking additional injury. I just don't know. I
fly for hours with no pain, that I know.
R