Tosh, Andrew,
I see your point.
On Friday I cleaned our Doctors Surgery. As the Doctors were turning in (Thery were quite impressed!) I asked them iff the backpack would be bad for my back. The opimiom was; No it would not, so long as I didn't bend too much. Most of the time my back is straight when normaly using the backpack, it's if you bend down your asking for trouble. Just remember; Bend ze Kneez!.
The problem, to me, is lifting it up and down or lifting the barrels to fill it. As you can see in my earlier post in this thread, I have designed my trailer to elliminated these problems.
The straps on ther backpack are however too thin and, as in another reply, I am sorting that out.
Thanks
David