If you have the XSD of the taget XML, I recommend XML::Writer XML::Compile. You have to mush your input data into the data structure corresponding to the output XML data, but that's all you have to do. XML::Writer will then create the appropriate XML from the XSD and your data structure.

I've also had good experience in creating a template using HTML::Template(::Compiled) and filling in the data from a flat datastructure, but that really depends on the output XML format.