This is roughly half the bed space we had and leaves roughly half the box area for other items.
If you scroll up you can see the mess we had on our last trip. With having a hatch style topper door it drips in the foot of the bed after 2 days you have damp bed that dose not dry till I get home and wash every thing. You will also notice the cooler sitting on top of the bed. So every time it is set on the ground dirt is picked up and set on the bed. 3 dogs transfer enough dirt we don't need to help it along.
The platform us a simple build using 2x2 and close to 3/4 plywood I believe it was like 19/32 or some odd mesurment. It has held up and all I did was cut the front section off and add a bit if bracing to the original setup.