If you stretch the covering before you tack it around the edges, you don't have to depend on the heat shrink action to keep things tight and you won't get wrinkles since it's already tight in it's original state. 

From 30+ years of experience with $kote......

Always use BALSARITE around the edges for adhesion.

Wrinkling is always caused because the film was not tight enough when it  was sealed around the edges. The trick on a wing is to tack down the center ends of the covering first (just like in their instructions) not the corners. Then the corners.  Then with very little pulling pressure tack down the trailing edge.  Now using your HEAT GUN, hold the leading edge film with a glove and while pulling it taught use the gun to tack the leading edge down.  At this point the covering over the span should look as though it has already been shrunk, if not repeat the last step again. Do the same with flaps unless you prefer to stick the covering to the balsa, which is a whole diffferent game.  Use you heat gun to pull the covering around compound curves a little at a time.

On closed areas like a built up stab make sure there is a way for the air to escape as it pressurizes inside from the heat because it will blow the covering up like a baloon and when it cools wrinkes will reappear after shrinking. Good way is to have the hinge slots open during covering or drill some small holes in the TE.

There is a ton of tricks applying $kote and they are usually learned by experiance over a long time.

Phil