Help needed first time ever aboard in mobile home

2012gee

hi we are travelling to Geisenheim in Germany our first time ever abroad camping and need help in finding campsites from calais to Geisenheim then we would like to go to Berlin, also do we need cheques we do not have a clue what to do here so all your help
would be great. we travel on the 11th July until the 26th. We are in Geisenheim 16th 17th 18th and 19th we have a site for then, but wold like to know sites maybe in Dunkirk then Belgium also is it safe to just park up and not be on al site.

Sorry for all the questions