They do still sell the double-knob one new, Roy. Vintage Trailer Supply has it for one example.
I'm not sure how thick the door on your trailer is, or how "smushable" the lockset is, but if I remember correctly it's made for stick-built camper door thickness, so you might need to customize something.
I can't remember on my double-knob one if you turned the inside knob to unlock it or if there was a separate lever. If it was a lever, it would have been a small, out-of-the-way one that the dogs would have a tougher time with.
I like levers for the same reason they allow your dogs to escape
; easy to open!