Has he said why? Maybe he is trying to say not doubled up on your light circuit or something?
The SatKing box pulls about 0.5A, so you shouldn't have any voltage drop issues.
The Sphere satellite box only needs power while it is deploying and closing - once done, it automatically turns itself off, so no power used once deployed. I haven't measured the current while deploying, will do if you need me to.
Who is the "SatKing guy"?
I have the satellite dish box and the SatKing box on the same 12V circuit, which is a subcircuit off the battery.
I put an inline switch on the 12V lead to both boxes so I can isolate the power while travelling so there is no danger of the dish auto deploying, but that's just me.
If you have a 12V circuit handly near where you want to install the boxes, I suggest you use that - the Winegard circuit is more than adequate (that's what I used).