There were these, I made and used these starting about 1971. There were mouse cages I bought from Dan Musseti(sp) I bought 150 a VERY LONG TIME AGO.
As we developed a need to house lots of snakes, it because apparent that "another method" was needed. My Snake cages were topnotch(the first drawer cages EVER) But what to do with hundreds of babies and raiseups. So the rack system started.
At first we used cheap shelving. And a cage like this,

In fact, this is one of the cages used. I still have that 100 or so lids(something the matter with me) They are in pretty good shape, I think I will, oh never mind.
We used plumbers heat tape in the back for heat in the winter. They for all intents and purposes were the same as a rack system of today.
We went from using them for raiseups, to housing adults and breeding them in larger cages. Then I moved to larger tubs for keeping them in all the time. I found some old blanks for the larger ones, but I must have sold all the finished cages.
With the larger cages we housed them in the tubs, but quickly learned to nest them "outside the box" which is something mostly missing today. This was done by me and several other breeders like Erine Wagner.
I later developed a very large an effecient nesting cage. I did this because as weird as it sounds, I HAD to be in west texas or mexico, at the very time my snakes were nesting. So I made Large deep nesting cages that housed all gravid females while I was gone. Man did that teach me alot.
From there the sterilite boxes were developed. And that was it for me. After a decade or so, I found that sweater boxes, TOOK THE FUN out of keeping kingsnakes, so I moved on to pythons. Which still HAD to be kept in cages.
I want to add, I learned everything from those large cages with drawers. After that, learning was downhill. Also, from those drawer cages, I announced that all you really need is the drawer and not the top part(the cage) I believe that was when the idea took off.