Fridge vent covers

All of the vents will have close to the same size screening.
Sounds like you are going to be replacing the complete unit.
Verify the size of the opening in the roof to insure you get the correct size.
I would try to use a long air nozzle to try to blow as much debris out as possible. Look on top of the refer to see if needles are laying there. A vacuum may pick some of them up from the roof.

There are metal one's and plastic one's. Get a metal one they don't break.

Well I have a norcold fridge and I know it's a norcold vent cover. While I had it off, I cleaned a LOT of pine needles off the screen, and I actually had to cut some of the screen to get it out of the way, because I had so many pine needles down on top of the cooling fins. I know that whoever had this RV before us, must have parked it under pine trees it's entire life

Vents are pretty much the same. I replaced mine with one that has a slope on front.
I would check to be sure that the refer installation is right. Many have been installed with too much distance between coils and exterior wall. Should be less then an inch.
I used foam board secured to fridge's framework with construction adhesive.