**BEWARE** Oahu is not set up for RVs or Camper vans. You will not be able to stay at any state owned campsites on Wednesday or Thursday nights, they are all closed. Patrick advised us of one parking lot we could stay at which is literally a lot on the side of the main road with a toilet block (less than ideal). I would also advise against staying there as the police told us you can be sited for sleeping in your car/RV unless you have a permit. The only privately owned campsite we found was completely booked up, so if you want to stay here book well ahead of time.
Also, the state campsites will require a 3 or 5 night booking. So staying one night at each site as you move around the island is difficult.