In addition, they should be capable of being jettisoned from the cockpit to reduce weight/impact on a vehicle.
Code-wise, these strike me as an entry-level craftable part of mechanics with the corresponding skillsets. I.E. Aero_Techs can make an aero specific drop tank & auto_techs can make a vehicle specific drop tank.
A final opportunity, drop tanks being modifiable by a skilled explosives expert to act as bombs which detonate upon being jettisoned and hitting solid ground - would be amazing.