anyone have any experience making their own heavy bag? I haven't used one since I was a teenager, but I'm building a ghetto ass gym in my covered patio -broomstick pull up bar, milk crate for dips, ropes for body weight rows, magnetic trainer for bike, propane space heater, greenhouse plastic for walls- all I need is a bag. I'm thinking a Navy seaman's bag filled with sand and wrapped in duct/gorilla tape will do the job. Any thoughts?