Yep, I am absolutely sure it is not the tubing. I actually removed the
tubing and ran the shower and fan for 8 minutes and condensation built
up in the fan. The fan was venting into the attic for this test.

Also I replaced the fan this weekend with a new one from Home Depot.
It's 110cfm and I am using the exact same materials (tubing and vent)
and I have no condensation in the fan.

I am very excited to have this project done and a working fan.