Sadly, it was a drive-by egging, and that part of the road is a blind spot. I won't say how/where it was a blind spot, lest I give away our weakness, but they are going to get away with it.
But we are now discussing how to cover that blind spot. This will not happen again. Hopefully. Or, at least, if it does, we'll be able to report their numberplate to the police next time. Hooligans! ("Get off my lawn!")

My husband and I are not
too upset about it, as our campervan was old when we bought it 6 years ago, and already has a few "battle scars". We're just amazed that people still do this kind of thing. Just ridiculous.