My wife and I spent 3 weeks at South Mission Beach, Beach Comber Coconut Caravan Park in August. Even though this is a Big-4 park it has only just been taken over and is not usual Big-4 standard, although they are upgrading. The sites are small and the slabs are very short, some will not fit a medium size rig plus vehicle. There are sites up the back, but they are grass and get very wet underfoot when it rains, and it will rain. The back sites are next to the road which is VERY busy and noisy. So, not really a good option if you have anything bigger than a medium van. However, I do recommend the restaurant down the road.
North Mission Beach is a much better area, it is close to the shops and most sites appear to be slabs. There is a Council caravan park as well which is next to the beach, but the sites are basic. There are other caravan parks in the area, including Wangaling Beach, but I am not sure what they are like.