we've got similar brackets on the bus and on the roof - then a small strap goes through them both to hold the roof down. Here's a couple of pics, not the best, but hopefully show you location etc
After my little roof off fiasco on the Severn Bridge a few years back, I too resorted to physical straps to retain my Houdini of a roof. Worked really well but became a bit time consuming when packing up from camping. I put up with it for a few years mainly using double sided fabric Velcro doing the same routine as your straps above until I could come up with a nicer alternative. I bought quite a few different types of clips and pins and toggles etc but just couldn’t manage a nice simple and quick release and attach method for ages. Eventually I cobbled together four over centre clips to hold it down which are super quick to use either upping or downing and I’m happy that my errant roof has met his match. I’ll grab a good picture later. But here’s the double sided Velcro just before it’s strapped down.
I have the same set up as Ben with 4 straps. They work really well, provided you remember to lower the roof
unlike I did on a 7 mile jaunt to Tenby South Beach last year 
Similar yes. I see Gary has some solutions
This looks solid but would be overkill for this job.
I'll call as soon as I can. This is just what I need.
