A lot of older RVs had Polybutylene plumbing, but I thought that was gone before 2001. There were lots of trouble with leaks with that system as it was more brittle and very weak against freeze damage. Many people pull it all out and switch to PEX.
I think I have identified it. I believe that the pipes are indeed PEX pipes. My confusion stems from the fact that my dealer sold me some incorrect gauge pipe. Still.... this is a very tight installation!!!!