Re: low tech sloution for pontoon cover.
Trust me on this one, DON'T DO IT. My first hand experience with North Dakota in winter is that it's very cold and you get a considerable amount of snow. What WILL happen is at least one of three things:
---The PVC will get very brittle in the cold. The snow load and / or wind will snap them like twigs.
---The weight of the snow will create enough downward pressure to push your side rails outward.
---The cover will rip to shreds from the weight.
Been there, done that. I suggest a wood frame with a healthy slope on each side to allow the snow to slide off before it builds up too much.