A set of Sniper lasers is a good start. With them you can check your camber and toe very accurately. You should set your caster/camber pills to their neutral position to start with and see if you’re even side-to-side with the lasers.
We don’t usually throw the lasers on every time we make a camber adjustment, we just turn the pills 1 dot at a time to dial the kart in.
He does not need to be in the kart. When you set the kart on the ground though, note that the camber will change slightly with his weight in the seat. Usually we see about 1mm more negative with the driver in the kart.