I cannot directly address a C Ranger tug, but I have used air conditioning in a 20 foot cuddy cabin. We used two different types--one was a cheap "Fedders"--one of the $89 Walmart types--in the doorway, with a Sunbrella fabric to close off the rest of the door. The other was one of the carry on units on a foredeck hatch. (much more expensive--and a pain to take on and off the boat.
There should be room for an air conditioner under some of the cabnets/forebunk--5,000 BTU should be enough cooling.
We sailed in the Caribbean for over a year total time, and never had air conditioning. But we were always anchored out, or at a dock where we had air flow. The wind scoops were enough, along with fans to keep us cool.
With trawlers on the Gulf coast, and our C Dories, we have air conditioning (the Tom Cat has an 8300 BTU RV air conditioner on the top--not sure that would look right on the tug.). We will run the air conditioning until 11 to midnight--usually by then the evening is cool enough that if we wake up, we just open up windows and hatches (with screens) and run fans, with out air conditioning. During the day, we find that the C Dory hard top is adequate for keeping in the shade.