Aren't those pretty heavy? And getting the weight up high by putting a load on top isn't good for handling. I've done quite a lot of camping in mine and have found that the 1200lb payload limit restricts my options in a hurry. I have to put the water and coolers in the back seat to keep weight forward enough to keep from ruining my rear springs when I run with 1000lb or more. That also keeps the weight low and the hit to handling is reduced. You cannot put 1200lb in the bed and expect the rear leaf springs to survive.
OP mentioned a Retrax cover, which appear to be 90lbs. Diamondback is 70lbs for both panels plus struts and center. Probably less than 90lbs overall and you can walk on it! Then with a retrax, you need a rack on top to put cargo on (you cannot mount directly to the cover) so it would be heavier.
Being able to walk on it gives you a way to load a rack over the cab, a spot to put your cooler or in my case, a way to transport stuff to my place in the mountains without losing my weatherproof storage in the bed. We have two German Shepard’s in the back seat so cargo spade is at a premium.
For example, we cut down our own Christmas tree. Normally this would mean putting our luggage in the bed with the tree meaning our luggage gets wet and covered with tree sap. Now, I just tie the Christmas tree to the bed cover and load stuff in the bed like normal keeping it dry and clean. Problem solved!
No matter what you do, you have to figure out the cargo weight limit. Easiest seems like Deaver HDs but that is a discussion for somewhere else.
Right now, my plan is for my spare mounted to the diamondback and a winch where the spare was. I may but a tent on a rack above the bed cover leaving more cargo space above the bed cover but below the tent.
I am not so worried about center of gravity since it’s not that much higher than what is in the bed. You want to avoid heavy weight far away from the Cg (in the vertical direction). Yes, it will hurt the Cg but I don’t see a way around this.