I recommend gluing all parts together as you assemble, with medium CA (or even better, epoxy) and sealing your stand with epoxy or clearcoat.
* when gluing stand together, I recommend clamping sides to braces while glue cures.
The Parts...
Assemble the rear box... Some of the parts are pretty tight fit because of some rounded corners so tap them in snug.
Assemble the front box...
Slide a side onto the rear box, then onto the front box... repeat for other side.
Install the boom tube supports with the supplied nuts/bolt/washers as pictured.
Install the propguard sides to the stand with nuts/bolts/washers supplied as pictured...
Finish by installing propguard backplate...
Install padding to protect tub... foam tape works well.
Adjust boom tube supports to correct spacing and height to best support your rigger.