The Casa de Campo is park/woodland, slightly west of Madrid centre with a big lake at the eastern tip of the park... zoom in on the P4N map and the name of the park will appear with several P areas surrounding the lake. Both the roadside areas and the car park are free. The road we used on the north of the lake comes up as Paseo Maria Teresa on the app but with a big van, you might be better in the car park to the west of the lake - Paseo Puerta del Angel. It's worth having a good recce around the quieter road areas first to see if there's space to fit, then come back to the car park if not. The roadside areas aren't uniform in size but we found a place where my 6m van fitted with nose towards the road, rear towards the lake, same as the campers nearby, so you could be OK parking side on?