Hi Leslie!
We leave in a week for a wonderful two and a half month stay at Disney's
Fort Wilderness Resort and I can understand your own excitement for such a a trip.
You can certainly put requests in for specific things but please understand that they are requests and not guarantees. But Disney does try to make the special magic for their guests and will do everything they can to make something happen to make your vacation a bit easier for you and your mother-in-law.
The first thing you will want to do is to call reservations at 407-WDISNEY and ask them to put your request on the reservation in the system. The other option, and I do recommend doing both, is to call Fort Wilderness directly and make your request with them as well. That number is 407-824-2837.
There is a preferred loop that is very close to the marina where you would catch the boats to the Magic Kingdom as well as the Wilderness Lodge and Contemporary Resorts. It would accommodate your 36 foot RV as well as be a fairly easy walk. Other loops would need for you to be near one of the internal bus stops along the primary roads. They would need to select a site that would be close and an easy walk to these stops. The internal buses will drop you off at the Pioneer Hall end where you have the marina and also the main bus depot area at the front of the resort where you would catch buses to the other three parks.
When you check-in upon arrival please also mention your request to make sure they have you in a spot that is easily accessible to transportation.
Hope you enjoy your Fort vacation as much as we do!