The campers are designed to be installed with the tailgate removed. If left on it will be in the down position, making it challenging to get in and out of the camper. Also, removing the tailgate enables easier access to the spare tire.
An exception to this is if a long bed camper is installed on a short bed truck. In this case the tailgate will remain on and in the down position. The camper will extend beyond the truck bed and over the lowered tailgate.