Camper looks like its not level

You have a camper with a weight of about 2500# with standard equipment. Adding personal items, any additional accessories, outdoor chairs, etc, can easily raise the weight to the range of 3500-4000#. With that weight I am surprised the springs have only dropped a half inch or so. It is best to have the camper sitting flat in the bed or the truck. That helps to minimize strain and any potential damage to the floor of the camper or bed of the truck. A board under the back of the camper would also leave the truck pointing somewhat upwards and the headlights would not be aligned and would likely blind oncoming traffic.

There are a great many potential solutions, including Timbrens, Supersprings, and airbags. You should also weigh your rig to be sure it is within the load capacity of the truck and especially fails within the load capacity for the rear tires. Again, suspension mods mentioned can help but you may also need to upgrade your tires to higher load capacity.