the rar folders are probably in index format, i assume they are numbered so if you double click the first one (eg. 00.rar or 01.rar) it will unzipe all of them into the directory you create for them (in there will most likely be a setup or image file).
I found a text document describing the details. All I need to do is extracting the .rar files to .../SourceMod/ folder just like any other Source mod installation. But there are like 31 folders with the same name, all with the of size of 204.800KB (moddb.com torrent).
Here is the downloaded torrent folder with 46 files (the ones you can't see are just named CM12.20_FULL)
CM12.20_FULL01 first , then after its extracted i suggest checking the size of the files, if the extracted size seems a bit small do the CM12.20_FULL02 (it might be 2 index's)