Look at the bottom of
this Rufkahrs catalog page. They sell a variety of positive latches. Scoll down to the bottom and you'll find two knob-like latches. The "L-5100" is, I think, the same latch that
Casita uses on their trailers. I bought a half dozen SL-9291 latches (at the bottom of the page). They are a smaller knob 2/3 the diameter (which feels half as big) of the
Casita latch; I felt they look and feel too petite, so I used another solution when I put new doors in my
Scamp. (Rufkhars didn't carry the larger latch at the time.)