I just "went through" my L-100 last week as best I could. The non-availability of parts makes it difficult. But after disassembling it and reassembling it about thirty times, it works much better, and I now have a pretty good understanding how it works.
My trailer is a bit older than yours, but the knob was not screwed to the side of the door, it was riveted with largish rivets. I think about 3/16". I believe it was that way from the factory, as it would require some sort of captive nut to hold a screw, and that just wasn't Airstreams way of doing things.
I can't give advise regarding the keys. I need them too. So hopefully someone will have some input on that subject. I have a special problem with my lock. It seems to be locked in the middle. So from the outside, the knob will turn one way but not the other. If someone (wife) tries forcing it, it binds up and I have to disassemble it to free it
I have been hoping to find a blank, and take it to a locksmith to see if they can make it work properly. I've been going to call VTS to see if they have any available, but I don't think they do.