Buy a set of inner bags, i know what you mean ref side loaders, the bags make it easy. Also, the bike was designed with those wardrobes on the side, it does make a handling difference so be careful what you put on it!!!!
It is possible to fit 1200GS panniers to a 1200RT,,BUT,it is some job,,u have to throw away some plastic,and rebuilt the taillight,,,or use the taillight from a 1200GS,,,,Like I did on the 1150..