There is nothing wrong per se with using global variables. It is just the way you use them that counts. If they are used to perform some spooky "action at a distance", then there is something wrong. But global variables used to set some parameters affecting the global working of your program is OK.

I tend to store these global parameters in a hash I call %config and many times I load it from an external config file.

Actually what you are doing is more or less the same, only you have gone one step further and use an object. So you just made it a bit more complex with no benefits to compensate for this complexity. Your way to get data in or out of your object is more difficult than using a hash. It does not protect you from any typos, since you do not even check in your getter method if that slot in your object ever existed beforehand and it is now being created silently (and perhaps wrongly).

I guess your idea is to use this global object to move data in and out of your subroutines without having to use any variable as parameters. I can tell you that is the wrong approach. Subroutines should have a well-defined input and output interface, which should be obvious to any programmer, i.e. the first line of your sub should grab the data in the @_ variable and store it in lexical variables (with meaningful names) and all data returned by the sub should pass through a return statement. A sub should not "leach" or "leak" information in any other way.