High there, i have a large TT and have found that it depends on the size of it, some TT are small enough to be classed as a standard pitch but, in the case of mine on a number of sites we get charged extra because it is quite big. we have even been charged the same as caravans.
heres one for you, as many know we used to have a cardinal, just changed to a caravan, now the caravan is the same size as the cardinal without the bed bits, so a month ago we went with friends to a site, they had there conway tardis and awning us with caravan and awning both with 2 adults and one child and dog we got charged more than they did!!!!!!