I'll second the recommendation of Hershey High meadows in Hershey, PA. We stayed there 2 nights ago in site #22. The site from about 20 to 26 or so are closest to the tracks. I would say there's an NS train about every 15 minutes on average. One time I say the Circus train go by. The local still uses a caboose as a shoving platform.
When I checked in the lady looked at the map, turned to her assistant, and said "Don't we have somewhere else we can put them beside right by the trains?" I said I requested it. My son and I love trains. She said "Oh, okay, if that's what you want."