Ron-

I have installed a safety latch on my trailer, as well as some others. It is a good idea, as the latch can pop open, generally ruining the door and often breaking the gas struts and/or their attachment points. I used a simple hasp type, and just secure it with a hitch pin, but you could substitute a padlock.

BTW, there are only a few keys for all Cobra trailers. Williams Soaring generally has the one you need in stock.