The standard Invoice Slip does not produce big enough characters, for posting via windowed 'Documents Inside' pouches. I do not use packing slips as that means 2 lots of printing.
 
I have modified the \templates\admin\admin_invoice_html.html
 
as follows -
change <!-- begin delivery_name_block -->
to
<!-- begin delivery_name_block --><strong><font size="4" face="Verdana">
and
 
change <!-- end delivery_country_code_block -->
to <!-- end delivery_country_code_block --><br><br></strong></font>
 
Anybody know of a proper way of doing it, instead of hacking the code ??.