There are at least two major elements to any cage trap, one being function, of course, and the other, practicality.  Once the function is in place in a trap that catches well, the trap has to be user friendly, not too heavy, not too large, but as small and light as possible and still catch, hold and hold up.

Within the world of practical is stackable.  In order to be stackable there must be no external components, all parts must tuck neatly inside the wire box.  What this comes down to is engineering, problem solving.  As an inside out ADC operator, in the business for a couple of decades with small animals and a lot longer on beaver, I ran into the same obstacles, situations everyone else does.  Understanding the problems is step one, then figuring how to beat them comes next.  It was from my background with cage traps that making a stackable trap with internal components a must, nothing less, which is why everything we make has nothing protruding beyond the confines of the traps to catch on other traps in transit in the truck or on brush when the traps are deployed.  You can even pile them up when setting.