Its been out of production for decades. Ebay, RV salvage yard, or measure and get something close.
Picture of what is on my 1977 1300. My upper vent is different than yours as well.
Your vents look like someone added them later, like the trailer originally had an ice box and someone wanted a fridge
. Original lower vent on mine is MUCH lower, probably at least three inches lower so the vent assembly is well below the raised section on the side. The placement of yours partially on the raised section and partially not is a mistake (hard to seal).
The top one on mine is lower as well, takes out the raised logo.
Your lower hole is really large. So the VT-24-1 is too small. You really need t fiberglass in a piece across the top, say 3", to get the opening well below the raised section, then get a hatch vent to fit. Matter of fact, find the vent first, need one that opens easily if you are using an old fridge
, as all the controls are accessed from that vent.
All the new ones I have found have rounded corners. If you want to maintain that look, you will need to do some fiberglass work, then find some salvage parts.