I can't answer your question directly, but will tell you to go to the "Camping at WDW" board here on the DIS and ask your question there. The FW experts can tell you anything you need to know, maybe even more.
I've moved this thread to the Camping at Disney World board. Like GOBA Mom Lynn said, it's the best place to ask questions about any of the activities that are available at Fort Wilderness.
we did this last year and it was family of 4 (DD7 &DS13) top 3 things we did that week. We loved it. Also, it was just something SO unique that you could not do anywhere else.
We also did this last October and enjoyed it although DD7 and DS8 thought it was "creepy". The ending was fun. It is a unique experience and very personalized service. Would definitely recommend it.
One recommendation I have is to wear bug spray. We got there early since I wasn't real sure where we were going so I allowed a lot of time and my lower legs got eaten alive while we waited for our carriage. After our ride we watched Hallowishes from the FW beach area. Great ending to the night.
There is a link in that report to a previous report about the Haunted Hayrides, which were offered before the Haunted Carriage Rides were introduced in October, 2008.
If you have any questions after reading those reports, feel free to post them here.
I did this with my parents last year. It was great! It was misting for most of the ride, which just added to the experience. Some of the beginning was a little dull, but once they got into the story, it was more and more fun. Plus I got to see parts of the Fort I'd never seen before, which was really nice.
Before when it was the hayride, there was a teen (maybe preteen) boy sitting near us who was udderly freaked out the whole time. It is scary and the acting is amazing, but when you know Disney won't do anything to harm you, it keeps your nerves a bit calmer.