To be honest I'm not a 100% sure, you can have it on top of the original mattress but you will have to take it out when the roof comes down, there is more information on the club shop, I will have a look if you like
Hi all just a update, I'm willing to take £130 for this and I will sort out postage at my expense, we are moving house and having a clean out.
Many thanks Jon
If it helps. We have replaced the VW upstairs mattress with a Zone Sleep Ultra and it fits fine with a good 1” airspace above with the roof down. Also it has a very open structure so less likely to become damp. Phil