I have a lot of hauling experience. I used to own a logistics/hauling company. You no doubt can adapt a GN ball into the bed of the CT. That's not an issue. The tongue weight is reduced on a GN in relevance to the overall weight when compared to a bumper pull. I have no doubt that even loaded that GN in the picture will have a tongue weight at or under 3500lb. The issue is the total weight of the loaded trailer. That is a dually tandem axle, probably rated for a minimum of 24k. The dual motor states 10k, and the tri motor states 14k. Neither will come close to pulling that trailer when loaded to it's max. It will pull it empty for sure. If he only hauls loads like in the picture, he should be fine with the tri motor. The dual would be questionable.
But also as stated above, maxing out the towing weight will severely reduce range. So that needs to be taken into account.