I've had some luck with those yard guard type sprays that you spray around the campsite. But, they work best on a day with a slight breeze so you can spray them up wind. There is a certain chemical in them that is the best and not all of them have it. But, that info is out in my camper and it's winter here in MN so I don't remember what it is. You also have to apply them correctly , in the trees, and the tall grass around the site you want to protect.
I have a friend that has a yard sprayer that works on propane and bombs the whole yard. But, at a park some of you neighbors might not like that.
I also found that a cheap box fan plugged into my camper outside outlet and blowing a breeze the correct direction on certain days will help out the problem too.
Around here the mosquitoes are at there worst at dusk. If you bomb them before hand and then wait until after it's dark to go outside it works the best.
Not everyday is the same. Sometimes something's work and sometimes other things work. It's a******shoot. Sometimes nothing works.