Solid materials, follow the installation video, it will walk you right through the setup. Make sure you use the spay bottle with dish soap to check for leaks!!! I thought my connections were tight, they were NOT. I found one small fighting that was not quite tight enough, the soapy water produced a noticeable bubble. I tightened the fitting and retested, all clear. I will recheck frequently on an upcoming 7 week road trip to make sure all is well. The big plus ARE THE GAUGES. No more guessing ho...