"...are flexing repeatedly or rubbing with movement of the vehicle..."

Our theory is that with an RV, EVERYTHING is flexing and rubbing all the time. Every time you move a RV it has been described (don't remember where I read this) the same as going thru a 3.2 earthquake. Unless you are driving on CA highways, then it is more like a 6.5. The only flex lines we have are from the regularors to the tanks, don't cost all that much to replace them from time to time. Everything else is ironpipe. We will or course keep an eye on them...