3 mo old requires a rear facing seat. Not sideways like the sofa, or forward like the co pilot chair. The only feasible place I would suspect would be a dinette, lap belted in the harness of the seat and facing backward. The problem I see with this is the seat angle being 90 degrees. You may want to check local law enforecement. Often they have folks that help with proper child seat installation. Maybe you could use the co-pilot seat if it swivelled to face the rear. Or if will attach facing rear with the seat in the normal position like a car.