My thoughts are you could possibly use (or take tips from) caravan "anti flap kit" which are designed to hold out the edge of an awning like your tarp. I think what you're aiming for is to keep the edge from flapping up and down which will cause poles to lift or pegs/ropes to loosen. But the gap in the two tarps is going to be tricky to get right, hard to keep them both at tension and not let water in. Perhaps all you really need is some rigidity to the tarp - but how "strong" do you go, before you know it you have a frame with a tarp over it, you may as well just buy sheets of tin and roof the damn thing!
My thoughts are you could possibly use (or take tips from) caravan "anti flap kit" which are designed to hold out the edge of an awning like your tarp. I think what you're aiming for is to keep the edge from flapping up and down which will cause poles to lift or pegs/ropes to loosen. But the gap in the two tarps is going to be tricky to get right, hard to keep them both at tension and not let water in. Perhaps all you really need is some rigidity to the tarp - but how "strong" do you go, before you know it you have a frame with a tarp over it, you may as well just buy sheets of tin and roof the damn thing!
Exert.
Ha!