Sleepy is correct, the COG is the balance point of the tc .
Therefore, if you place a SB camper on a LB truck, the campers COG is still in the same place as it is if it were sitting in a SB truck.
The campers rear overhand prevents it from sliding too far forward, it has to be blocked at the front by using a storage box or wood frame block .
The added length to the trucks bed is between the cab and the rear axle, not behind the rear axle and the bumper.
People do put SB campers on LB trucks and the campers COG is still at he same point in relation to the rear axle.
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COG spread sheet posted by one of our members