I have a platform in my Element. These pictures may give you some ideas
http://www.pbase.com/paulj3/elementplatform
On the Element, front and rear seats can be lowered, forming a continuous, though somewhat lumpy bed from front to back. I removed the rear seats, replacing them with a 4' long platform. When the front seat backs are lowered (and slid all the way forward), I have a sleeping surface about 8' long. We sleep on backpacking air mattresses, with our heads and torsos on the flat rear half, and feet on the front seat backs. The dog and gear are stored on the front seat bottoms, and on and under the dash.
On the road, gear is stored under the platform, in the 'foot well' between platform and front seats, and on the platform. I add a bungee 'net' across the middle of the platform to keep gear from sliding forward. Plus some boxes are strapped down.
The platform itself is built from wood boards, plywood panels, slotted angle steel, and 1/4" hardware. So it can be easily disassembled and stored - though I haven't removed it completely in a couple of years. It is held in place with turnbuckles.
paulj