Ice Fishing Shack Camper
There is a company in Canada that manufactures Ice Fishing shelter out of polyethylene. They are rotational molded making the body seamless. Here is one installed on a truck
Here is view of the inside.
As you can see there is shelf and two bench seats. There is a plywood floor that cover the holes used while ice fishing.
My uncle used to build campers for his Toyota pickups and after a bit of use, cut a hole in the floor, add skis and tow them out onto the ice as ice shanties. Then after a few seasons of that, they got towed out into the woods for use as deer blinds.
To him though, their most important use was for fishing.