The medium I use to form the molds is Permatex RTV Silicon Gasket Maker. While the High Temp is not needed, the red color does photogragh well. Available at most auto parts stores, it retails for about $8.00 a tube. You can get about 4 port molds from one tube. I have tried other silicon caulks, but none worked nearly as well and as fast as the Permatex Gasket Maker.
Tap Plastics Mold Release Wax is very helpfull to ensure a proper seperation of the mold from the port surface.
A smooth surface and a putty knife are used to mix the silicon before application to the port. I use a small piece of melamine and a plastic putty knife.
A small, chisel shape brush, about 1/2" wide with stiff bristles works well to apply the Silicon to the port surfaces.