Picture from:
http://www.postadsuk.com/automatic-toyota-previa-converted-to-camper-hampshire_212324-4.html
http://www.garagetunerautomotive.com/2010/10/build-a-bed-in-your-previa/#+
Picture below from Angie Edwards:
..."working on a budget of less than $100, so I will add more later.
That is a normal full size single bed, with a really comfy Sealy innerspring mattress, heaps of storage underneath and I can sit on it without hitting my head on the roof!.. picked it up on Gumtree for $40, and there is still room for my kitchen at the back."