I missed some of the early discussion. I'm glad you got a bike you like. Did you sell the XtraCycle? Sometimes one can do better on Craigslist than selling at the shop, or via consignment.

I have a kid's trailer that I use for moderate cargo loads, and a flatbed that I use for the big loads. I designed the flatbed to go with my custom cargo bike, but pull the kid's trailer behind an ordinary bike.

I do have some large duffels that I'll occasionally tie to the cargo bike, but I find the trailer may be more handy than the extra cargo capacity on the bike.