American manufacturer Northstar ships flatbed-style popup campers to Australia. I don't have a good photo of the popup model. Northstar also makes a full height hardwall camper for a flatbed on a full size pickup:
This photo of a standard slide in camper shows the amount of enclosed storage space you gain when the side walls of the camper are extended down to the flatbed.
It's also possible to add several storage compartments below the flatbed.
You might have to change the shore power inverter from 220V to 110V for North American use, but otherwise I think the Northstar export models could be sold for use in USA.
Chip Haven

This photo of a standard slide in camper shows the amount of enclosed storage space you gain when the side walls of the camper are extended down to the flatbed.

It's also possible to add several storage compartments below the flatbed.
You might have to change the shore power inverter from 220V to 110V for North American use, but otherwise I think the Northstar export models could be sold for use in USA.
Chip Haven