I've made this pattern (from the first Mason Dixon book) before, and it calls for a double strand of bulky weight yarn. I thought I would try it with worsted, just to see if it would work. After all, the Fiber Trends felted clogs are made with a double strand of worsted, and they hold up great.
I made the largest of the 3 sizes in the pattern so that the finished box wouldn't be too small. It was awfully floppy before felting.
I had to felt it for a long time. I let it go through an entire wash/rinse/spin cycle because I had given up on it. In the end, though, I pulled and prodded and I think this is a giftable box after all. The walls aren't as sturdy as those in my other boxes - you can compare wall thickness in this photo. If I loaded the green box up with needles like this red box, the walls would bow out too much.
I'd like to experiment with this pattern a little bit more, perhaps with a triple strand of worsted weight yarn. Or... even quadruple? And I think I might go back down to the medium size box.