The most challeng part of building the platform is how to deal with the removable section. This section has to be securely supported when in bedding, also need to be easy setup; secondly this section including supports must be not interference with the slide back seats, and also no interference when seat back tilt down when in driving mode.

I over throw a couple of different solutions, this one I believe is the best to me.

This removable section(2 small piece, one of is table) one side is supported by first 2x4, the other side is supported by metal rod ( not shown in this picture , see previous post). The metal rod two ends hanged to existing metal knob ( for hang up folded back seats). I'm afraid the rod and two knobs not strong enough to take the whole weight, my option is adding middle support. See the pic, that why first 2x4 attached a T. On the T, there is arch shape cutoff it is for he rod swing when seat tilt or move back. (rod will swing around the hanging point)
Generally speaking, as long as throw the two boards away, the seats are freely move back forth, tilt up down, the rod will follow the seat moving. 
When setup for bedding, simply move seats forward, put two small boards in position, that's it! Ready to go.