What is an 'installation fee' on a french site?

Marleyarchie26

This year we're going to an area without a Club site close by so I've found an independant caravan site.  The tariff shows an 'installation supplement' of E2,50pn, but after emailing the site twice (in broken french), they've still not said what it is so
I don't whether I need it or not.  They say there is no extra for utilities, waste or booking fee, but there's no mention of an awning fee anywhere (and we are taking one).  I've asked the Club but they don't know either, does anyone know what it is?