If the tank is ahead of the C.G. than balance it empy. If it is rear of the C.G. balance with the tank full. This way, as the tanks empty the planes balance will change into a more nose heavy condition, which is not a big deal. If it moves to a more tail heavy condition you may find yourself in trouble.

This is how I have the electronics set-up on my 28% Laser 200 with Brison 3.2:

1.) Ignition strapped to bottom of the fuselage immediately behind the firewall. I also went with a shielded Bosch plug cap.
2.) Ignition battery (4.8v 1650 mAh NiMH) strapped to right side of fuselage just behind the firewall. Its corresponding switch is about 3-4" behind the battery.
3.) Receiver battery (6.0v 2700 mAh NiMH) and switch are in the same locations on the left side of the fuselage (directly opposite the ignition battery and switch).
4.) Throttle servo is located 3" or so behind the ignition switch on the right side of the fuselage, connected to the throttle lever with Sullivan golden rod (the black one in the white sleeve).
5.) Receiver (Futaba 149DP PCM) behind everything listed above by several inches at the rear of the hatch. Antenna is run through a tube tied to the inside of the fuselage.
6.) Fuel tank is in front of C.G. right now but I will be installing a smaller tank and will place it under the wing tube on the C.G.
7.) Elevator and rudder servos are in the tail.

This set-up has worked great with no interference problems.