What does your reservation paperwork say.. in total.. not just site 87. Does it say anything about even if a numbered site is provided, that the campground reserves the right to change to another, equal site?
I personally would call first instead of writing. If you talk to them, in a calm, reasonable manner, maybe they can ask the other folks if they wouldn't mind moving, given your situation.
I get the idea about writing, because there's a record, but a personal touch works better sometimes. You can then follow up via email to confirm the phone call.
Mike
