I agree with SeaDog, dish soap and water will kill them.
People say Hedge Apples will repel them and spiders, you're supposed to put them around your foundation or base of your camper and they supposedly keep them away, I tried this several years ago at an old farm house we lived in and it did not make a dent in then number of Box Elder bugs on the side of the house.
I've also used a residual bug killer on the side of the house and it seemed to work pretty well, killed the ones I hit and kept others from landing on the surface so they all moved on.
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