The best way to find campsites is on the BC Marine Trails map. There are number of excellent campsites on each leg of the Salish Sea Marine Trail:
Leg One: 52.6 km from James Bay Angler Ramp to Rum Island. Some campsites are: D’Arcy Island, Sidney Spit, Isle de Lis
Leg Two: On this 92-km stretch the Salish Sea Marine Trail duplicates the central route of the Gulf Islands Marine Trail, running east and north of Salt Spring Island then along Trincomali Channel through False Narrows to Nanaimo. There are a multitude of side routes, possible, of course, with one being the inside route along the west side of Salt Spring Island through Sansum Narrows, as well as side routes through Stuart Channel taking in possibly the communities of Chemainus and Ladysmith. There are many campsites to visit. See the map.
Leg Three: 84 km from Newcastle Island Marine Provincial Park, Nanaimo, to Friendship Park, Sechelt. This is the wilderness section of the Salish Sea Marine Trail, with much of the most dramatic shoreline and isolated locations. This is where to go on the Salish Sea to get away from it all. The trick is the open-ocean crossing to get here, which can be placid to downright dangerous depending on the weather. This makes it a fairly advanced route, but with attention to the forecast and timing moderate skill levels should have no issues if they can manage the distance of the crossing – about 10 km whether from Vancouver Island or the Sunshine Coast. Campsites include Pebbly Beach, Buccaneer Bay, Home Bay, Farm Bay, Long Bay
Leg Four: 59.8 km from Friendship Park, Sechelt, to Jericho Sailing Centre, Vancouver. This leg combines some great mountain scenery and the fjordlike setting of Howe Sound, the Big City climate of Vancouver and the expansive beaches of the Lower Sunshine Coast. If makes for a varied but imposing area to traverse, involving both a major shipping area (Burrard Inlet), an open water section along the mouth of Howe Sound and a lengthy shoreline journey along the Lower Sunshine Coast to position yourself to or from the crossing of the Strait of Georgia. Campsites include: Plumper Cove, Apodaca Provincial Park (in the works)