Have Crowbar installed

1.) Go to steamapps\common\Left 4 Dead 2
2.) Make a folder called !Custom_Sounds
3.) Go to steamapps\common\Left 4 Dead 2\left4dead2
4.) Open Gameinfo.txt and navigate to the bottom. Add 2 directories above the "update" line. It should look like this:

SearchPaths
{
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ !Custom_Sounds/!p5r_music_pack
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ !Custom_Sounds/!SoundScripts_BASE
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ update
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ left4dead2_dlc3
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ left4dead2_dlc2
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ left4dead2_dlc1
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ |gameinfo_path|.
Game‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ ‎ hl2
}

5.) Save the changes made
6.) [OPTIONAL] Create a shortcut of Gameinfo.txt & Copy/Cut it
-Go to the !Custom_Sounds folder
-Paste the shortcut of Gameinfo.txt into this folder
7.) Download SSMB (Copy the Steam link and go to the "Download" tab in Crowbar)
8.) Place the file in the !Custom_Sounds folder
9.) Unpack the .vpk file (via the "Unpack" tab in Crowbar) You'll get a folder called "Unpacked 0.XY"
10.) Rename the "unpacked 0.XY" folder to !SoundScripts_BASE
11.) Download the P5R Music Pack mod from Gamemaps[www.gamemaps.com]
12.) Place the file in the !Custom_Sounds folder
13.) Unzip the folder, then unpack the .vpk file & rename the folder to "!p5r_music_pack"
Both mods are now installed

1.) Delete the folders prefixed with "!"
2.) Delete the lines added into Gameinfo.txt