In the photos below you will notice 3 covering irons.  One trim iron and two regular irons.  When covering you need lower heat to tack and attach the covering.  Then HIGH heat to shrink.  You can find these regular irons at swap meets for $5.00.  The tack and adhere temperature is VERY important.  Too low, and needless to say, it will pull loose. To high.... and it will want to shrink at the attachment point. (NOT a good thing)   Notice the el'cheapo stand I use to face my "cool iron" flat up.  This allows me to lay on my Coverite Thermometer to make sure of my temperature before I use it.  http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXB352&P=7 This is the important iron.  About heat guns! You may notice no heat gun in the photo.  That is because on the last 2 planes I have built or recovered, I have NOT used one.  I tried cardboard shields, wet paper towels, etc,..to keep heat away from seams and attachment points. The gun just does not work as well for me, or easier, as the HOT iron I keep handy.   (set to covering specifications).  By having 2 irons going I do NOT have to wait for one heat up, or worse yet, wait for the iron to cool down.
This was the most useful 5 bucks ever spent!! Next to that, is the $5 spent for the thermometer.
I may ruffle some feathers about my views on the heat gun.... but it could be just me.  Covering does take patientce.  I found myself using this as a "speedy" way of shrinking.  I have improved my covering jobs since using my heat gun to shrink "heat shrink tubing" on my electric wiring!!    ......  lownslo.....