I was "quite liberal" in bedding my tanks. I used 1 & 1/2 tubes. So 2 would do it.

I guess that the important part is to get a good amount in between the spars and the tank flanges, so the tanks ride on a good layer of silicone. There is a fairly large, increasing gap as the tank moves away from the spars, which I do not think we have to completely fill. After they dried, I turned the wings over, and I put a "finishing bead" in that gap near the spar to make sure I had enough there to handle the "twist and torque."