I plan to have a peak around when I replace my head unit, but I imagine that pulling off the dash is going to be miserable. Also you wouldn't want to compromise the passenger side air bag's functionality somehow.
Off the top of my head I believe it is 70"x 54". Full width starting from the rear doors and endjng just in front of the wheel wells. So sleeping sideways in the van there is room for someone who is 5'10" like me.
Here is the bed being cut out of a queen sized topper for scale.
Also here is the trick to making the insert: cut one half of the bed out so it sits perfectly on the frame
Now take 1.75" off the inside. Cut this out so that you wind up with a scrap piece that looks like a carpenter's square.
Copy that piece
Measure the rectangular gap and cut a piece .5" shorter and .75" narrower to allow for the carpeting.
Now when you go to the foam put the C together. Add the carpenter's square piece to trace the inside of the C. This will create an overhang that is flush to the frame.
(Otherwise your legs would be on the 2x4 frame when you sat down.)
Take the foam square and line it up so it is flush to the front edge and centered side to side. One complete everything will slide in and out easily and be flush.
Finally I think I over engineered with the removable cross brace. The bed seems plenty sturdy without it. With 2 people I'll probably be happy to have it though.
Modified the doors for towing mirrors after work today. Not bad at all to do.