What's your budget?
You have two options. You could just get a Burley Travoy and call it a day. Pick up the other bags for it and you'll come in around $380 for the trailer, bottom mesh and upper mesh bag.
Other option would be if you bought a Douze cargo bike. It separates at the mid point. So a 8 ft bike is cut in half to 4 ft. The Douze comes in around $4k.