only took me three days...
the hard part: drilling a hole to align with the hole on the car.
Build T cross bar. Cut longer than the measured distance to ensure a very snug fit. This (and all) pieces are removable.
Add mid support / arm rest with notched side and removable front and rear supports.
add 3 ply (light weight and gives good support) plywood cut to size. drill dowel holes on the sides and back (helps stabilize arm rest). add carpet. add piano hinge. two front support braces are on a hinges and one is free standing that fits into driver's seat runner.
trimming the 2X4 should not be your last step... but it was mine.