Which license plate to use? Truck camper's or trucks plate?

I've just go to say WA state has a weird law. You have to register a big box you haul around in your truck? And this big box needs a license plate like a motor vehicle?
Do you also have to register and license truck tool boxes, truck bed covers, and loads of firewood?

Some transitos & parking cops will remove the rear plate & take it hostage. Since many states & provinces do not have front plates and they are used to this, simply move the front to the rear and put a vanity plate on the front. Stash the rear plate with sticker on it. I do this every year.

Stash the camper plate & move the truck plate up there. Just don't forget to move it back if you take the camper off the truck.

Truck Plate!

no. Why would anyone have to do this?