Mammoth a couple more thoughts-
I hear ICBC and their enforcers are pretty strict on not exceeding mfg. door sticker weights if given the chance. Are you going to get stopped and asked to weigh if your rig does not look like a waddling tub going down the road? Prolly not... but weight is not your friend off highway boondocking nor at the gas pump.
Anyhoo pickup style campers by nature of their design to wing over a pickup box can only carry so much heavy stuff low down - the more weight you add “up high” the more moment of inertia there is to contribute to swayage and rock and rollage. I think roof units weigh in the 80-100lbs range?