Portsmouth to St Malo always used to be our preferred crossing but it became quite expensive. We now prefer to go to the east side of France so tend to use the Dover/Calais crossing.
We first stayed at Le P'tit Bois in 1986 when it was a nice quiet site with a decent toilet block although we could only get tepid water in the showers!! It had no other facilities then. We last visited the site in 2004 for an overnight stop and found it very busy and expensive. Furthermore the showers were still not particularly warm.
We prefer Camping de la Hallerais at Taden near Dinan, particularly because you can walk from the site into Dinan, along the River Rance. Again we have not stayed there since 2004 so cannot really comment on the site.