I double stacked 330s in a deep narrow channel one time because every time the beaver approached the high set trap up stream, it swam under it, and when he approached the deep set down stream, it swam over it.
He ended up ducking the top trap of the double set and got caught in the bottom trap.
I danced on his grave with true glee in my heart.
The deep/narrow is key. Deep, narrow, grooved runs can be stacked. The bottom trap will be hit first, then following beaver will swim over the first and be caught in the top. In my area there a few ponds with clay bottoms where this can apply. Probably better off just setting single traps a few feet apart. Less fuss