In response to your questions, I tried the experiment on my 83 Scamp
. To answer your two questions:
1) Yes, the door will close with the pin in it, and lock you out.
2) Yes, if the door is locked from the outside with the key, it can close and lock someone IN. You can not open the door from the inside as the latch will not retract enough to clear the strike plate. The door has to be unlocked with the key for them to get out.
The one thing that I found annoying with the locking pin on the chain is that it swings while traveling and mars the door finish. To stop that, I put a small magnet on the side of the latch to hold the pin. Problem solved, now just need to clean the marks. Pics attached.