Unless you have spiders falling from trees above the camper, all you need to do is spray around each item on your camper that actually touches the ground. for example, spray the ground around your tires about a foot out each direction. Do the same with your stabilizer jacks, everything. No need to spray a parameter around, just a parameter around each object touching the ground.
Not much you can do when they come from "above" though, or where the wind blows their webs to, or what falls from a tree.