Best Way To Treat/Filter Campground Well Water???

100-1 it's not bacteria. Wells are generally bacteria free as there normally isn't a source of nutrients and commercial wells get regular testing. They would be shut down if there was a bacterial problem.

Rotten egg is typically sulfur in the water. It won't hurt you but will taste & smell nasty. Hot water heaters intensify the smell.

No real good solutions. You can mess around with charcoal filters and water softeners but they usually only make it slightly less objectionable.