My Tiger 60 has not had the rear fuselage side panels removed and yet it wasn't hard to balance. I don't think whether you leave the sides solid or remove the panels will matter much from this point of view but I do think it makes a difference to the strength and rigidity . If you are flying off grass I would recommend that you use wheels of at least 3 inch diameter in fact mine are 3 1/4 Dubro light weight . The model taxies and tracks well on takeoff even on uneven surfaces.
Tim