Had an interesting experience while prepping our 5er for a trip and thought I would pass along the info.
Went to unlock the trailer's deadbolt latch and the key just turned 360* without moving the bolt. Tried putting pressure up and then down while turning but no joy. Sat there deciding whether or not to break a window. DW opined that the entry door glass was probably the cheapest to replace.
However, on our Cougar, there is an escape type fold out window next to the entry door. After studying how the window is mounted, I removed several short self tapping screws along the top of the hinge and was able to carefully tilt the window away from the frame. Using a long #2 Phillips, I was able to reach down to the bottom inside of the window and unfasten the folding latch bar. With the window out, I was able to push the screen in off its clips and then raised the shade. Reached around the valence and was able to unlatch the door from the inside. No broken window!
Now for the FYI - If you are blessed with one of these deadbolt locks, you might want to remove the inside door plate and check to see that the 2 countersunk Phillips machine screws are tight. The screws fasten a plate to the back of the lock. This plate is what keeps the little linkage rod that connects the deadbolt key and lever to the actual deadbolt in place. The screws were loose allowing the plate to move and the linkage to fall out. I guess our trip back east rattled the screws loose inside the lock. Tightened with blue Locktite. FWIW