waterproof backed fabric pieces (Dunfermline KY12)

These were from small garden chairs or something - the edges are finished/ bound. The second photo shows the waterproof backing fabric - looks like woven nylon. There are 3 pieces - 32 x 42 with channels sewn in both ends (ie you could put a rod through each end); 36 x 50 with channel at one end, the other is raw edged; 36 x 92 with channels at both ends and a reinforced middle strip.