@Debbiedt6 There's plenty of room given this is a SWB... The picture shows the seats where we would normally have them, with the mattress topper on the shelf behind the seats. New Wave use an OEM California bed and rails but modify them to fit on the correct side of the van for a conversion.
There are some notable differences to the fitment as the rails are positioned about 20cm (I think) further forward than those in a California which means more rear van space when required. I know a mountain bike fits without the front wheel needing to be removed... I've not tried this in my van but I have seen it in another New Wave van. The other neat difference is that the shelf behind the rear seat is made of bedding slats rather than being solid. This makes the bed super comfy and they can be removed, rolled-up and bagged should I want to push the seats all the way to the back of the van.