You could check the door frame issue and confirm your suspicions by measuring the door opening, diagonally, from corner to corner. A frame that has been pulled out of plumb will have two different measurements. I would also climb underneath the trailer and pull a string from front to back along the frame. A bent frame will show up quickly against a taut string. It might be that the popping sounds you heard were huck bolts or attachment tabs giving loose on the frame. And, maybe not. I don't meant to alarm you but it would be something I'd be investigating.