Many epithelial surfaces have natural coating by polymeric materials, e.g. mucus. Foreign materials may be introduced for coating, e.g. for lubrication or drug delivery: examples are vaginal gels delivering mucosal antigens or topical microbicides. We present here a next generation biophysical vaginal coating model, which supersedes our previous work. The model characterizes the vagina as an elastic tube with a flattened lumen. The walls have porous surfaces through which natural vaginal fluid transudates, contacting and diffusing into a gel coating layer within the lumen. Spreading of the gel layer is driven by gravity and other trans-luminal pressure gradients, and wall elasticity. Gel rheology is characterized by the Carreau constitutive equation, including the presence of a yield stress. The model determines the local dilution of gel as water is transported into it, which is linked to local dilution and time-dependent rheological properties. This association is obtained experimentally. Gel coating flow is computed, accounting for variable properties at each spatial location and time step. A set of current and prototype microbicide gels is being evaluated. Results show the predominance of yield stress at later times during flow; the flow ceases when remaining vaginal wall distension is insufficient to develop shear stresses that exceed the yield stress. Dilution is most important near the vaginal walls and the leading edge of the spreading bolus. It is there that dilution proceeds most quickly, where the local viscosity of the gel drops most, and where spreading accelerates most. For the test gels, there are trade-offs amongst the dilution-dependent yield stress, limiting low shear viscosity, and rate of shear thinning, in rates of epithelial coating. Practically, these provide flexibility in optimizing gel compositions for target rates of epithelial coating. [Supported by NIH AI48103, CHRP ID07-B-135]