Point the van up I-215 to Lake Perris, the State Recreation Area lake toward Riverside, for the closest honest overnight to Menifee. You sleep in a paved hookup loop with power and water, a short walk from a buoyed swim beach under the Bernasconi Hills, with rocky Alessandro Island out in the lake to paddle to. The one thing to plan around is summer heat, so book a site with electric and bring your own shade.
Swimming and climbing at Lake Perris
Lake Perris runs 8,800 acres against the Bernasconi Hills, and it is one of the few reservoirs out here you can actually get in the water at. Two lifeguarded beaches, Perris Beach and Moreno Beach, are roped off with buoys; the reservoirs near Temecula and Hemet keep bodies out of the water, so this is the swim day.
On the west shore, Big Rock is a 180-foot slab of granite that draws climbers into the morning shade. The state does not install or maintain the bolts on it.
From Menifee it is I-215 north to the Ramona Expressway exit, then east into the park. The hookup pads are 31-foot back-in spaces and your rig cannot cross the space lines, so this is a campervan loop, not a place to squeeze a 40-footer. If you want more beds than a van, size up to an RV. There is no shade on the loop worth counting on, and the park recommends bringing your own canopy for summer.
Where else the van goes
For wine country, Temecula Valley and the campground at Lake Skinner sit south down I-215, a separate trip laid out on the Temecula campervan lander. The desert belongs to Joshua Tree, a longer haul east and its own campervan lander. The rest of the state is on the California hub.