Yes you can order these for exterior use also or get galvanized spray paint and coat yourself
The BCS2-3/6 is sized for a triple 2x beam to a 6x post. If shimming out the double 2x to fit the cap, the built-up lumber (multiple members) must be fastened together to act as one unit to resist the applied load (excluding the connector fasteners). This must be determined by the Designer. Thank you!
Depending on the connector being fastened, Simpson has specific fastener recommendations...in this case, Post connection should be made with 6 x SD10112 screws and Beam connection should be made with 4 x SD10112 fasteners.