Here in the USA, big box home improvement stores sell patio furniture (chairs, etc) constructed with PVC tubing. If UV degradation is a concern, maybe a coat of white enamel would protect it? I know that there are special UV-protective paints used on carbon fiber and other composites when placed out in the sun.
Personally, I’d go with galvanized steel. My Sky is up on a 6 meter galvanized steel tube and it works well…