Regardless of which FM trap you select, it needs to be between the antenna and amplifier. In the case of a mast mounted preamplifier, that's the outdoor unit, not the power supply/insertion block. The goal is to stop strong interfering FM signals from ever getting into the amplifier where they would be distorted and mixed with other signals to produce yet more interference.
I like the idea of shielding the RS from the elements. If one is a bit handy, a bit of ingenuity can use any number of recyclables to fabricate a rain guard. Then there's the trusty Coax-Seal and Scotch 2228 that does a great job of water proofing connections.
http://www.amazon.com/protects-types.../dp/B0002ZPINC
http://www.homedepot.com/p/Scotch-1-...2#.UXd7T0of-hQ