There’s a very simple solution.
Cut a 2x10 to fit across left and right into the slots your truck bed already has for that reason.
It will do double duty. Put it across the front of your truck bed when the camper is in… that something you should be doing anyway, it helps spread the load across from the camper if you have to do a moderate to hard brake slam. The front walls are very thin and delicate and bend easily.
Then when the camper is off, move the board to the slots at the rear of the bed and it becomes your tailgate.