Ok, lets just say for chits and giggles I weigh..aaa..lets say 260. With the camper suported on the same structure as if it was in the bed of the truck not secured ,if there were 260lbs in the master ...
The overcab part of the structure is mostly an empty shell with just a mattress, a few clothes and supplies, and however many sleepers you'll have up there. Compare this to the rest of the structure, the appliances, gear and supplies, the holding tanks and contents, and propane tank(s). You should see that it would be hard if not impossible to put enough weight in the overcab for it to tip.