A lot of stuff scrounged from old bags and cases is chrome tanned , which is more corrosive to steel than vegetable tanned . It doesn't wet mould well , and will rust the heck out of your stuff if it gets wet . 6-8oz vegetable tanned is the best long term bet ( oz per square foot ) . Most stuff you scrounge from old stuff is about 3-4oz , and is often made from split leather . Most of the structural strength is found in the grain .
Chris