The laser interferometer space antenna (LISA) mission uses laser interferometry to detect and observe gravitational waves from astrophysical sources. Modelling of LISA ultimately needs to forecast and interrelate the behaviour of the science input, structure, optics, control systems and many other factors that affect the performance of the flight hardware. These models include high precision STOP (structural-thermal-optical) analyses. In addition, self-gravity analyses of the spacecraft, based on the structural-thermal modelling results, are required for each analysis cycle to understand the gravitational interaction between the spacecraft components. The complete analysis cycle is called STOP-G. Several aspects of this analysis require unprecedented precision due to LISA's challenging design requirements. We present here a modelling approach designed to minimize analysis errors, particularly those that enter when mapping results from one modelling step to the next. Central to the approach is the use of a single model topology for all phases of the STOP-G analysis cycle. The feasibility of this approach was verified using a simplified model of the LISA spacecraft.