The Mass Properties analysis follows the component priority rules and will compute the masses and inertias from individual bodies into the total. Components may have volume density, surface density (mass/area), or a combination. However, as of version 3.31.1, interior thin surface densities are ignored by the analysis, regardless of priority. For example, a tank of priority 1 with both surface and volume densities modeled entirely within a fuselage of priority 0 will only contribute its volume density to the mass while the surface density is ignored. To get around this limitation, a step-by-step approach is recommended in which different priority levels are analyzed separately and accounted for.