While Dennis always has great input we stayed at the railway RV park and took the train. That said we had our son and his friend 12 and 10 with us and into trains, so the ride was good. We enjoyed Williams as it was summer and they had western shows each night on old route 66 and it was a short walk from the park.
If you are not into or have kids that are into I agree with Dennis the train is kind of a nonevent. I can assure you there will be freezing temps from about Halloween through Easter at least. Went through fall of 12 and stayed in Williams overnight and had to disconnect water because of freezing over night.