Yours.... I re read your post. I see you mounted the fans to the top vent, which is ok but not ideal. The optimum place to mount them is directly in front of the condenser (as physically close as possible to it) blowing out and letting the exhausted heated air vent through all the louvers.
Additionally, you might want to add additional unfaced insulation around the cavity sides, between the outer cabinet and the fridge body as FR tends to skimp on insulation (IOW cheap out). A roll of R13 unfaced is about 8 bucks at Lowes, money well spent, I stuffed almost 1/4 roll in my cavity, FR had maybe a wisp of insulation in there.......
One other thing you want to address is airflow as it comes up from the lower vent cover and exits the upper vent, being propelled by your fans (I used a pair of Fluid Dynamic Bearing 120mm CPU fans, totally silent, low amp draw, the pair pull just under 1.2 amps at 12 volts).
You need to insure the airflow is a smooth as possible. I presume you have a Dometic fridge. Dometic specs an upper baffle plate (that FR is lax about installing, like the single fan and insulation...)
You need to insure you have an upper baffle that wraps around, behind the condenser and curves upward and fastens to the outer/inner wall studs so the airflow is not impacted by the loose insulation (turbulence) in the cavity.
Because the upper vent is plastic, mounting the fans to it will amplify any operating noise they make, whereas mounting them close to the condenser via a wood crossbar, dampens any sound they may produce...you cannot hear mine run.
I have mine running via a snap disc thermostat, 80 on 70 off (WW Grainger or Dell City Electronics), 7 bucks, attached to the outer outboard cooling fin on the condenser and picking up 12 volts from the terminal block that feeds the control board on the fridge itself.
I added an ATO inline fuse holder as a safety measure with a 2 amp ATO spade fuse.
That way the fans operate independently of the fridge and run only when needed (mine cycle on and off especially at night due mainly to the fact that my fridge shuts down at night because it has reached and is holding my preset temperature.
I actually did a test with a recording remote digital thermometer and published the data on another RV forum, but suffice to say here that my freezer stays consistently at -2 to -4 degrees (F), no matter if the sun is beating on the fridge side or not and no matter what the ambient air temp is outside. and my fridge compartment holds 34-38 degrees no matter where the sun is or ambient temperature and cool down to that temp went from a day to 5 hours and the fridge cycles on and off once it reaches the preset temp. Last season I had to run my temp control at maximum to maintain 40-43 degrees fridge temp. Not now. I run on setting 4 (6 total settings).
Running mine on just propane, I started with a full 20 pound bottle and ran it continuously until the bottle was empty never shutting it down.
It ran for 36 days continuously on a single 20 pound bottle, pretty economical I'd say.
Rule of thumb is the closer the fans are to the condenser and the smoother the airflow is, the more efficient the ammonia unit becomes.
When RV builders started installing ammonia fridges in slides, they never took into account the natural draft effect a lower vent / roof mounted exhaust vent creates, but then I never expected them to consider the natural draft effect. Too much for them.
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