On a hot day it might run 45 minutes per hour, which equates to about 1.9 amps
per hour.
I have an older Engel MRFT-540E-G4 and I am sure it uses more than 2.5 amps max in real world use. It is a 2000 model , the first with a fan and 134A gas. My electrical connections are initially by 4 G x3 metres, then 8 g by 2 metres so I have very little voltage drop from my 130AH second battery. I cannot find the current draw of my model but the REALLY old ones ( MRFT-540A up to 1982) draw 4.5 amps max

First even with a new Engel rated at 2.5A ( and that is the steel body, the plastic is 2.75), a car is a very hot environment and in the tropics I believe they run up to 100%, as their insulation is not all that good even in a bag.

The other thing to remember is that the 2.5 amps is with a full battery at 12.7 or whatever. Once your battery gets down the current required increases. At 11.5 volts the fridge will draw 2.75 amps.

So the upshot is that if you use a fridge normally, opening it to get out drinks, putting fresh warm drinks in, my experience tells me that you will not have enough charge capacity, even with a new low draw fridge.

My wife loves the solar as I let her put stuff in during the day whereas before I was always insisting to reload in the early morning when drinks were left out overnight to cool..
Regards Philip A