I also agree that you want to consider all the costs. Don't forget that you need an appropriate tow vehicle, a place to store your camper, and insurance. We also have a pop-up and tow it 1,200 miles to WDW each year. We have the wheel bearings repacked every trip (recommended every 2,000 miles) and need to keep an eye on the tires (proper air pressure and get new ones every three years ... blow-outs on the interstate are not fun!).
To address your question about making a reservation ... As early as you think you might be going is not too soon to book. Many Florida residents will camp on the weekends, so weekends (especially for basic sites - water/elec - 2000 and 1500) can book up before the weekdays do; thus, making it hard to book full weeks at the last minute. To book a site-only reservation, you just phone WDW reservations and make a room-only reservation ... only one nite's deposit is required and then you have up to 5 days before your reservation to cancel. Should a discount code become available, you just call them back and have the code applied. If you are booking WAY in advance, they may not be able to tell you the exact cost, but it will be close (e.g. booking for Spring 2007 will be at the 2006 rates and then they will notify you of the correct amount when the 2007 rates are established).
We have been camping at WDW many, many years and actually prefer it to staying in a hotel.
Again, camping is not for everyone - but Ft. Wilderness is definitely the nicest campground I have ever stayed at.
). I do know, however, that the comfort stations are very clean (almost cleaner than at home!!, well, maybe not, but you get the idea).
