Old-growth Carolinian forest at Rondeau Provincial Park opens onto a Lake Erie beach, with the woods behind you and marsh on the bay side of the spit. The campground is in the park's north end, on roads named for those trees.
Ontario Parks calls Rondeau a world renowned bird watching destination, and the spring Festival of Flight is when migration hits the spit. Birders fill the north-end campground for those weeks, and summer beach weeks fill it too. Both seasons fill it, so lock the overnight first and treat the van as the second booking.
The park keeps one campground in that north end, with sites from tent-only to large trailer and electrical hook-up on some of them. If you need more sleeping space than a campervan, look at RVs for rent in Chatham. Camping runs spring through fall, and Morpeth is the town for the park.
Erieau is the next place on this shore.
Erieau
Erieau is the peninsula village on this same Lake Erie shore, with a lighthouse pier at the harbour mouth and boats docked along the marina. The marina sits between Lake Erie and Rondeau Bay, so a day from Rondeau is a walk on that pier and a launch onto the bay as much as onto the lake.
Marsh walking is the other half of the day, on trails at the edge of the village. Chatham-Kent maps the Erieau Marsh Trail, the Erieau Boulevard Trail, and the McGeachy Pond Conservation Area Trail as that network, and Blenheim is the inland town people name with Erieau. Erieau has no public campground of its own, so you sleep at Rondeau and spend the day on the pier, the marina, and those trails.
Farther west along Lake Erie, Wheatley Provincial Park and Point Pelee National Park are a Windsor campervan trip.
The Thames through downtown Chatham
The Thames through downtown Chatham is the paddle, a town day on the river past Tecumseh Park. Chatham Docks sit along the Thames in the middle of town, a short walk from the park. Boaters coming in from Lake St. Clair enter the river at Lighthouse Cove.
Pinery Provincial Park is a London campervan trip.