it's not good.....

The output of your script is:
The string - 'My PHP Class' in encoded format is : TXkgUEhQIENsYXNz
The encoded string - 'TXkgUEhQIENsYXNz' in original format is : My PHP Class

When i go to: http://www.base64decode.org/
and paste: TXkgUEhQIENsYXNz
It returns: My PHP Class

I do not see why i need your 'Custom String Obfuscate' package, because a simple base64_encode in PHP does do the same?

You probable meant the output to become something like:
UEhQQ2xhc3Nlcw==TXkgUEhQIENsYXNzZG90T1JH

But that's not good also.

If you strip the first two chars, and paste 'hQQ2xhc3Nlcw==TXkgUEhQIENsYXNzZG90T1JH' in http://www.base64decode.org/

The answer is: 676W0My PHP ClassdotORG

This gives tooo much details of the original text.