I originally saw "Punch Trunk" in the compilation film "Daffy Duck's Quackbusters", and I've now seen it in its own form (or should I say "I SEEN IT!"?). It was one of Chuck Jones's many completely outlandish shorts during the Looney Tunes/Merrie Melodies heyday. My interpretation is pure conjecture, but I get the feeling that the cartoon may have been an allusion to things like the possible UFO landing in Roswell; it seems like the sort of thing that could never happen, but what if it could? Just how would we respond if a five-inch-tall elephant started walking around the city?
But like I said, that's just my interpretation. The cartoon was probably intended as pure entertainment (and it is fairly funny, if not Jones's best cartoon ever). As it's not readily available on video or DVD, you can watch it on YouTube.