I've got two of the pioneer 12k units- they are very similar to mr cool. In that rv, i would guess you will pull 400 to 600 watts for 90% of the time it's running in cooling mode. Once it cools the room off, it can put out cold air using as little as 250 watts. That should give you about 2-3 hours for every 100ah 12v battery you run. I would bet 4 would get the job done on an average summer night here in the south.
These mini splits are killer! They SIP power compared to a traditional ac. And so quiet compared to a rv rooftop ac!