I’d stay away from the PVC ones. If you can fabricate/weld, I’d recommend hitting a scrap metal yard and looking for a air compressor tank. They already have pressure relief valves, bungs for air inlets/hoses, etc. If you are DIYing your shower, that will get you going cheaper than buying a “Road Shower”. Even easier would be to buy a Battery operated shower (Ivation- on Amazon) and a turkey fryer/stock pot. Multi-useful in camp. A lot less money/involved than a DIY shower.