There's a guy that I drive past every day here on the Isle of Wight that has one as well. I may pop in and say hello and see how he is coping.
for strength on these things the poles need to be redesigned
for apex strength but walls are still weak
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for wall strength and apex strength 2 different approaches to strengthening the walls and apex left side 1 design easy to build right side another type
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its only way i can see that sort of frame being strengthened for higher winds time
you need something like tube clamps to fasten to what you already have but thin wall tube or 1" box section would do its connecting from round to square but easy enough to make up with a plate and strap on end of tube
Try sailmakers who make covers for boats, or anywhere that does tarps for lorries.Now.... just got a find someone to make the covers