Hey, i work alot with pvc (commercial sparky) and you will probably find some issues with bending the pvc without getting a kink (depending on the angle), you can buy bending springs but they are usually only a few feet at longest. Try first with a few lengths before you commit your money to something that doesnt work.

I have seen commercial tunnel greenhouses before and they used steel rods about 3m long, 20mm^2.

Good luck