The OP did not say anything about not having a key, he said he couldn't get into the 5er.
We had this happen to us in March 2017, on our annual pilgrimage to South Carolina for our anniversary week. On the way home, I stopped on the side of the road (to let the dog out ... of the truck) for a potty break. Decided to get a couple drinks from the camper. I put the key in the door and the locked turned 1/8 of a turn and jammed. I fiddled with it to get the key back out, but no matter how I tried, I couldn't get the key to go back in the slot.
We were scheduled to spend the night at a KOA, and decided to go ahead and pull in there, but before checking in, I'd work with the door a little more. If I still could not get it open, we'd keep driving through the night and get home about 16 hours earlier.
I got my tool box out, and found some thin steel wire I had. I made a looped and pinched it, then was able to finally shove it in the key slot and wiggle the tumblers up and down. I could hear it when they finally gave. I could then insert the key and finally turn the lock open.
Since the door handle had 2 lock (one for the handle and the other is dead bolt), we just locked the dead bolt next morning and came home then.
But it was a bewildering experience to say the least.
About a week later, I went to my local RV dealership and bought a new door handle assembly (About $60), and 6 screws later had the new one in place.
Fortunate for us, the cat and the dog were in the truck, not the camper.
So you know, we had an extra key (actually 2 of them) available but they would not work. So it's possible something similar happened to the OP.
Besides, it's kind of hard to lock a trailer door from the outside without a key!
