I'd imagine that the wolves that he shot outside will be a distracting snack while he sneaks out. I don't remember if the herd was coming from that same side of the RV or not.
And as for Glenn and the idea that he was underneath and covered with guts, I'd have to watch it again, but wasn't he screaming during the whole thing? That would draw their attention for sure. That and the pileup of walkers would continue digging through the flesh right to him. It's not like they stop the second they hit spine and ribs, knowing that their meal is done. If he walks away from this, they better have one hell of an idea up their sleeves, because its going to take one.