Not good news. The topper arrived today, I gave it about 3 hours to partially expand and then gave it a try in my pop top. Total failure. Just before the front clamped shut, the back popped up. So I pulled the topper forward to hang over the gap by about 10" (to reduce the material at the back) and it again popped up at the back before the front could clamp down.
Given this was with the topper only partially expanded it clearly won't be any better when fully expanded.
So now we need to decide whether to keep it anyway, and accept having to remove it every time. Or, return it and buy the 2 narrow 5cm (but more expensive) toppers. More comfortable, perhaps, but even more bulk to pack in the boot when driving.
Very disappointing given Duvalay say "Designed to fit the Volkswagen California Beach, Ocean, and Grand California, its slim-profile design allows it to remain in the pop top during travel, reducing storage requirements." and repeated this to me on the phone.
Note: mine is 2021 6.1 Ocean. Maybe Beach or the older 6.0 had more room?