PSN packages can be launched directly from XMB without any backup manager.
I suppose that the purpose of converting it to game folder is to start the game from an USB device (FAT32)
Probably the easiest way to achieve this purpose is:
1. Create a folder GAMEI in the USB device (FAT32)
2. Extract the PKG and put the files inside PS3_GAMEI
3. Copy the rap file to /dev_hdd0/exdata or /dev_usb000/exdata
4. Refresh XML & reload XMB (note: the option GAMEI must be checked in /setup.ps3)
5. Mount the game with webMAN MOD.
6. Launch the game from the debug icon ★ PlayStation®3 (aka ★ app_home/PS3_GAME)
The next time you want to play the game, you only need to perform the steps 5 and 6.
NOTE: The games with files larger than 4GB cannot be copied to USB devices formatted with FAT32.