If you are buying from a main dealer, then I would suggest making any purchase conditional on them replacing the bellows with 06S, under warranty.
We had two sets of 03S on our 2023 Ocean - the first set leaked like a sieve under torrential rain conditions and whilst Aquatex may have helped, the volume of water ingress was such that I wouldn’t want to rely on it. The second set of 03S still leaked but less severe. Currently we are on 04S with Aquatex and they have been fine, but still yet to have exposure to a really prolonged heavy storms. My plan remains to get a swap out to 06S ahead of warranty expiry. Unless you have 06S it feels like whenever the forecast says rain then you will sleep with one eye open - that’s how it feels having been through the first major leak that we had.
Not sure how easily the dealers can now convince VW to pay for the swap out, but there was a reason that VW made 06S and didn’t stop at 04S !
A topper will help of course - also with insulation - but I have yet to use the one that VW gave us including in a couple of recent trips when slept up top in -1°c without any real discomfort thanks to a good Outwell duvet.
On the plus side the issue we had with the leak, whilst horrendous at the time, has absolutely not diluted our love for the van and the experience of owning it - it really is a superb piece of kit