I presume you're talking about the Mains Socket on the kitchen unit, and not the Inverter Socket at the base of the B Pillar behind the passenger seat.
Mains Hookup at Campsites vary from 6 amps, found on some Continental sites, to 10/12 amps or 16 amps on UK sites and some main Continental sites.
You can use Double or Triple adapters as long as the power consumption does not exceed the Amp rating of the site. Power consumption = Wattage of Appliances / 240 v.
For the 12v cigarette type socket you can use multi adapters. I have 5 sockets + 2 USB plugged in with adapters to charge 2 phones 1 an iPhone, Kindle, iPad and my in van WiFi router. The socket is fused at 20 amps and the adapters I use take about 10 amps if all in use, which is only when travelling or on Mains Hookup.
http://www.ebay.co.uk/itm/3-Ports-1...031203?hash=item211fc69ea3:g:c~oAAOSw44BYLryq