This is how I've done it in FSX.
Under the AddonScenery folder I've created a folder called:
RTMM
Inside that folder are all the RTMM sceneries listed in alphabetical order.
In the sim I've activated them ALL one at a time, starting with the last scenery which for me is Yakhoun Lake Cabin. This way they all show up in my scenery library (accessed via the FSX menu) in the correct order... A-Z from top to bottom. If another scenery comes out I just add it, activate it, and move it into position according to it's starting letter.