I seriously question the advice you've been given. Sounds like someone went a bit overboard. The key point is that you'll be portaging a bit of weight at various times during the trip, and that it would be a good idea to start improving your fitness level. There is no reason you should be "training" with a 120lb pack. Focus on general fitness, stamina, upper body strength, and ideally (but I don't know where you live) do some hiking in the hills with ~50lbs on your back 8-10 miles per weekend. This is a scout trip afterall. (If you insist, however, any reasonable backpack suspension should have no problem handling 3X 25lb sacks of lead shot... I have a couple tons on my garage floor if you need to borrow any <img src="/ubbthreads/images/graemlins/smile.gif" alt="" />)