Will it overlap the sides are be flush with the bed? I guess I was imagining a step side. For ultra light weight, there should be no floor, just three sides and some spars to hold her together below, like a camper shell. These spars could double as supports for a sleeping loft. Are the boys too tall to sleep sideways across the bed?
For the screen, you could do an enclosed three wall set up that went over the tailgate only with lean out poles in case you're on hard ground. Better yet, do the entire thing in roll up canvas, but shaped like a tear drop with bent electric conduit for a frame and shower curtain rings to hold up the canvas.
If you make a solid slide-in light enough and with a floor, it could become a portable cabin. You could lift it out and set it in place.
Time to go home....
