This paper presents a disturbance feedforward control strategy for active vibration isolation systems with internal air mount dynamics. First, a parametric model of an air mount system including a Helmholtz resonance is derived, which is an extension to the widely used massless spring-damper models for vibration isolators. Second, a self-tuning feedforward controller is proposed that fine-tunes the parameters of the model online. This refers to zeros only because the poles of the resulting controller are fixed in orthonormal basis functions to obtain preferable convergence properties. Simulations show the effectiveness of the control strategy and the sensitivity for estimation errors in the poles. It is shown that disturbance rejection can be improved up to 40 dB by taking into account the internal air mount dynamics in the feedforward controller.