Can you Recommend a Campsite Near Harwich Docks?

Sailing from Harwich in a week or so....

Will need to stay overnight as the ferry is 0900 in the morning (dont know how much time to allow to board?)  so we need an overnight campsite as near to Harwich as possible (with Rolls Royce amerities of course)

Has anyone stayed at a site near to the docks?  do you have a good one you can recommend (or a bad one to warn  me away from)

 Any comment appreciated as its the first time I have done this crossing

pete