Okay, I know how to spell both hole and cat but just decided to make it interesting. Here's how it went, first I traced the tube on his side, then selected the right dremel cutting tool, well this part was a crap shoot and lucky guess.
It took me a fair amount of time because my dremel wasn't fully charged and the fiberglass was differing thicknesses, which caused me the most problems. The hole wasn't quite big enough so I had to charge my battery for 2 hours before I could do anything which put me mid afternoon. I'm keeping a close eye on time because a snow storm and very cold temps are on the way and I want to finish.
Back outside with one hole cut, I'm thinking now how do I get a hole on the other side whichneeds to be fairly accurate because my tube is cv pipe with no forgiveness. I decided to trace from the inside of the pipe through the cat then drill four points through the cat on the inside to outside. Then I trace my pipe between the holes. After I that added about a 1/2 inch all the way around so I wouldn't have the super tight fit like the other side.
Worked beautifully and to my utter amazement I actually got the length of the pipe within a 1/2 inch on both sides sticking out. That's fine because I'm securing with clay now I need to start my diorama in the pipe. When that's finished I will be painting the cat......finally. BTW look outside that's today, it did arrive as scheduled.