Unzip the "GCR - Multi-OTT" and "GCR - Multi-OTT Side Chaining" files into this directory:
C:\Users\[USER]\AppData\Roaming\REAPER\FXChains

Unzip the "GCR - Global Slider" and "GCR - Multi-OTT Controller" files into this directory:
C:\Users\[USER]\AppData\Roaming\REAPER\Effects

Have fun!