I am almost done with my diy Blackcat tarp. I am at the point of deciding to use trim or not to trim. Do you use double folded bias tape or is there something better? Also does the trim serve any purpose other than cosmetics such as does it add strength? I took my time and my hems look perfessional so if the trim is just to cover up crooked seems, I'd prefer to show off my handy sewing abilty.