I should have added that anything that would physically fit into the key slot would lock/unlock the door - the cylinder was definitely toast
I was more amused that the key provided with my trailer, while it was likely a key to some trailer out there, couldn't have gone to the lockset attached to my door.
Making the FIC lock fit was not an easy task, cutting the hole in the door is the scary part (and I have not glassed the edges of my opening yet - it's on my "to do" list along with a gazillion other things), but I was able to basically fix a block of wood on the closet cabinet where it meets the trailer shell and attach the striker plate that came with the lock to that - it is secure enough for me (I wasn't going to go overboard with reinforcing it - because the reality is that our
fiberglass trailers are flexible enough that it would be a simple task to pop the door open with a prybar anyways, no matter how "secure" I made that strike plate).