In the gasket set there are 3 different gaskets for the back of the oil pan to the rear main cap. Those two rubber ones in the picture and a square cork one that I like to use. I never have any luck getting the rubber gaskets to not leak. If you use the square cork gasket do not use the rubber one. I like to take the square cork gasket, trim it to fit and glue it on the rear main cap with Permatex high tack sealant. I also use the high tack to glue the pan rail side gaskets to the engine block. I then put RTV silicone gasket maker on the back side of the glued down gaskets and square cork. I then put the pan on and torque it down.
Once everything is torqued down I fill the void between the back of the pan and the rear main bearing. With my finger I try to push as much RTV sealant as possible to fill that void. Leave it sit for 24 hours. Then retorque the pan bolts again.