How to rig a rain tarp without trees -- poles, maybe??

During my much younger days, I built a hang glider using 2024 alloy Aluminum tubing. You can choose diameters & wall thicknesses so that they slide into each other. Very stiff, very light weight, but pretty expensive. I've used left over pieces for masts, etc.

By the way, schedule 80 pipe or conduit is thicker (and, of course, heavier) than schedule 40, but is still both heavier & more flexible than thin wall 2024 Aluminum tubing.