Take his file, then copy what is in it into the file named CIV4UnitInfos.xml in the Assets\XML\Units folder at the end just after the last time it says </unitinfo>. Then, change the bit which says UNITCLASS_AIRSHIP to UNITCLASS_ZEPPELIN, and where it says UNIT_AIRSHIP to UNIT_ZEPPELIN, then go into another file in the same folder called CIV4unitClassInfos and add the following text just after the last </unitclassinfo> tag:
<UnitClassInfo>
<Type>UNITCLASS_ZEPPELIN</Type>
<Description>Transport Airship</Description>
<iMaxGlobalInstances>-1</iMaxGlobalInstances>
<iMaxTeamInstances>-1</iMaxTeamInstances>
<iMaxPlayerInstances>-1</iMaxPlayerInstances>
<iInstanceCostModifier>0</iInstanceCostModifier>
<DefaultUnit>UNIT_ZEPPELIN</DefaultUnit>
</UnitClassInfo>