I did something similiar, used a office chair box, went to the stores asked for their used shrink wrap and packed the crap out of it. I have had that same target for 3 years now, if a piece of the cardboard gets shot up I just cut it out and glue on a new piece. Plus it is big enough I can put the paper bow targets on it of the bear, elk and deer and give me something else to shoot at.
Joe