This is a little toolbox mock up that I've made. It has a working opening lever mechanism as you can see on the photos, and a lid with a handle. The lid is made from two parts. The two parts are to be welded together. The lid is designed with printing tolerances in mind.
More about how to assemble it in the assembling section...
Stick the part with the handle through the bigger part so that the six pins stick through the six holes in the handle part. Flatten the pins with a soldering iron to fixate the handle part in place. Optionally fill the gap between the two parts with whatever glue you think is appropriate. Doesn't seem to be necessary though.
Stick handle through lid
Same principle is to be used to secure the levers in place. Only there you should take care not to inhibit the free movement of the levers. Push the levers over the pins and carefully flatten the pins with a soldering iron. Wait some seconds and even more carefully try to move the lever until it either breaks free or snaps. If it did the latter, print the parts again... It should be enough to just flatten the pins a little so that the levers can't fall off of them. No need to make them too tight.
See the photos for how to arrange the levers for the mechanism to work.
Lever mechanism; how to assemble
Lever mechanism open (browned filament comes from soldering iron too hot)