How many draft truckers to save gas?

I would seriously advise against this. If you cant see the trucks side mirrors clearly your way too close. Truck drivers hate it when you do this and a lot will intentionally put you in a ditch. And anyone dumb enough to draft a big rig at 10 feet deserves to eat a bumper or be in a ditch. At 2 feet your not gonna live and Im not sure you deserve to after doing something that moronic.