We have been going to Fort Wilderness for eight years now. We have been there in a 40' 5th wheel with a long-bed F-250 dually and now in our 40' motorhome towing a Jeep. They have redone the sites in the last couple of years to make them wider and an easier angle to back into (the vast majority of the sites anyway).
If you are assigned a site and you do not think you can get into it or you just don't like it, you can request a different site. We have done this many times. We just pick an empty site we like, call the front desk and tell them we would like the empty site. It has never been a problem.
Some of the loops (300 and especially 100 and 200) are tight for big rigs, but I see them in there. We have stayed in the 300 loop in the past, but now request not to be put there because just driving around the loop can be tough around the curves depending on how people are parked.
We were there a couple of weeks ago and stayed in the 600 loop. Very easy to back into, lots of space. There are plenty of 40'-45' rigs in Fort Wilderness in all of the loops. The streets in the loops are narrow, but we've never had a real problem. You just have to take your time and be careful.
There is a nightly sing-a-long, campfire (s'mores) and outdoor movie. There is a pool with a waterslide and a hot tub. You can take the boat to the Magic Kingdom. You can rent bikes, motor boats, canoes, fishing poles, etc. You can play volleyball, tetherball, tennis and more.
Can you tell we love the Fort?