I promised some comments on container hacking, and since I have about ten of them done, I guess I have decided on my method.
First, a few comments on building them without hacking. Be sure to cut away all trace of sprue burrs on the parts. The little grooves that help alignment are very small, so the burrs can keep pieces out of those grooves if you are not careful.
The back and front pieces are large enough, and thin enough, that the panels bend enough so that they may not sit in those grooves while the glue sets. Be careful of this.
Now, for the hacking. I cut down a vertical notch in the front and back faces with one of those PE saws to get a thin cut. I then score the horizontal cut with an X-acto knife a few times, then bend it to break the section out. I also cut the neccessary containers from the side pieces by scoring and breaking.
The top piece has to fit within the side and front & back faces, with the top sitting flush with the faces and side. So I cut about 30 thou away so it will sit inside. The first few ones I did I glued pieces of styrene to the faces so the section of the top would not slip down too far. I did this when I was gluing the small, cut down section of the top in AFTER the normal top section.
I found if I glued the remnant in BEFORE I glued the rest of the top (the part over the unmodified faces), I could then get underneath the short section and push it back up if it went in too far. This eliminates having to glue the styrene pieces to the faces. The long, unmodified section fo the top goes in after the short (cutaway) section is dry.
I cut a strip of 0.020 styrene to the height a container and use this for the side of the topmost containers rather than fitting the piece I cut from the side. That piece is way to thick to glue on without recessing, which is a pain. Even the 20 mil stuff is a little thick but it is not too noticable.