Based on your profile picture, your RTT is rack mounted on rack in a truck 6+ feet off the ground. With my RTT trailer mounted, I only have to get my dogs (ranging from 60 lb Belgian Malinois to 110 lb Ridgeback) up about 4 ft of ladder. By placing my Yeti cooler (very stout) at the base of the ladder, they are able to hop on top of the cooler get into the tent with not too much effort. It took a little coaxing at first, but once they got it it was easy. They would much rather sleep in the tent then on the ground.
Get creative with your gear and you might throw a length of plywood that fits in the bed of the truck (1' x 5' perhaps) that you can use to build a modified ramp up a portion of the ladder high enough that the dog can get into the tent with not too much additional effort.