Try using a heat gun (I bought mine from Tower Hobbies) to tighten the covering on your Avastar. A Hair dryer just doesn't produce enough heat. The heat gun, which looks like a hair dryer, works well in open spaces such as on the wing and tail assembly.
Use a "heat iron" for areas that have solid wood sheeting such as the front part of the fuse on many all-wood planes.

Caution: Don't hold the heat gun over an area for too long as the heat can actually burn a hole though the covering.