My 03 was center steer and it ran best on the top end with a little more weight on the left side. It would lean to the left just a little at rest, but would level out over 90 mph. I had 2 optimas in the left side compartment and 1 cranking battery in the right side. That gave me right about +30 lbs on the left side.
Prior to that 3 batt setup, I had a 2 batt setup. 1 Group 27 in each side. THat balanced perfectly level at rest but leaned to the right a little over 90. A cooler full of drinks on the left side brought it back to level on the top end and gave it just that slight bit of left lean to the left at rest that i described earlier.
If you've got a side steer 03, it'll probably take a little more weight on the left side to counter your weight. In a center steer, the passenger doesn't really matter....just put him/her in the back centered behind you. Now that I've got a side-steer 21, I keep a shot bag in the boat. It goes in the passenger side rod locker when I'm solo, and i move it to the drivers side when i've got a partner. That seems to work well so far for me.