I have my Roti on an 18" kettle. I have a hard time controlling temps because of all the openings. I can usually get away with using just one basket because it so small. (bigger chunks of meat I'll use two)
You are cooking a Pork loin, not the tenderloin right? What size is your Performer? You have 2.5 lbs of meat? Give it a go with one basket. I'd bet you could do it.