Apply the sizes which you took of the A/C unit to the ripstop fabric with a marker. Use spray on glue or Beacon FABRI-TAC glue to apply the re enforcing fabric to the outside of the tent. NOTE: its easier to collapse the tent and pull it taught so there are less wrinkles when gluing the fabric on, I used some heavy lead I had laying around. This reinforcement will help so when you cut the hole out of the tent it will not start to rip the tent (thus the name Ripstop)
Once the fabric is applied and the glue is set well you can cut out the tent material in the middle of the reinforcer.
Now you could put the Ac unit in the hole if the fit is right, Mine fit perfectly with small gaps around the bottom and it cooled off the tent very fast, the OAT (Outside Air Temperature) Was approx. 89 F and the inside was below 75F within 2 Minutes.