I've just got an old 1/2 ton bulka bag stuffed full and stomped down with old shrink wrap off the pallets we get at work.
Since this photo was taken I've put inside another 1/2 ton bulka bag and given it a new lease of life. The old one had been outside for well over a year and was going good, had had 1000's of arrows in it, then my middle son started using it as his knife throwing target. That buggered it pretty quick, hence the need to re-cover it.
With no more knives chucked at it, my guess is it will now last ages before I might need to simply jam it into another bulka bag.
Best
Lex