I can sort of see how they could pull it off.I've been hearing some chatter that maybe Glen is not dead. Imagine the hoops they are going to have to jump through to make that even somewhat plausible given the circumstances. Lol. I suppose he managed to get away from the hundreds of zombies that were all over him and squeeze himself under the dumpster, where even a person as tiny as me could barely fit? Lol. Okay.Suspending belief for the show is one thing, over the top ridiculous story lines are something else though.
Glen is a smaller, wiry guy. That, combined with his life-or-horrible-death situation could possibly give him the incentive he would need to get under that dumpster any way he could. I doubt that any Z's would be "smart" enough to try and crawl in after him. They've never shown any to do either real climbing (they pull/push obstacles down) or crawling (except legless ones), so if Glen got under the dumpster, he'd likely be safe until the herd got lured away or distracted by some other active prey.
Far-fetched? Yeah, but it's one way it could be explained.