Hi Jim, sorry I have been away from home for a few days and missed your message. The pop top is by
Jerba Campervans and is their own design. It uses straps and also a metal pull down catch that you have probably seen in the photos. It's a belt and braces approach but seems to work well.
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The guys at Jerba have always been very helpful and I am sure if you drop them a line they will be able to help with a part number for the catch system. It uses studs bonded into the roof but I guess you could make something up to retrofit one.
I believe its by
SouthCo and like the one in the link but I can't see a part number on it.