You should find a lot of availability for Gatlinburg in March, since it's pretty early unless you want to see snow. I wouldn't recommend anyone plan a vacation there until April or May, when you'd have reliably good weather and lots of flowers and blooming trees to look at.
Tree Tops is a very nice resort, but they are still rebuilding from the fires and were always hard to get into on exchange. Many of the owners use their weeks every year. I decided to throw one of mine into the rental pool this year just to see if the demand puts some money in my pocket. It should be all finished by next March. A brand new resort, practically.
I haven't been keeping up with the progress on rebuilding other timeshares and hotels, but Westgate had a second fire recently, so I'm sure availability there will be tight once the seasonal demand picks up.
Sheila