Step 1. Download the PERP_Content.7z file
Step 2. Put the .7z file on your desktop
Step 3. Open Windows Explorer
Step 4. Goto C:\Users\(Your username)\(Desktop, downloads, ect.)\(File name)\(Steam folder name)\SteamApps\Common\GarrysMod\garrysmod\downloads
Step 5. Put the 7z file in downloads
Your done!
If any problems occur, tell me in comments.
Thanks my friendz.