I often have to carry things that are too big for the trunk, typically a large box. I've been putting them on the seat and using a net or bungees, using the side box handles as an attachment point. That doesn't always work well for the strap lengths, and it seems not so secure. Are there any good add-on strap options or other tips you guys have? I have a bungee net and a couple of adjustable/stretchy straps on the bike so far. I'm also considering some adjustable bungee cords.