Good call on the iron. I bought several OTC high end irons and tested them with a thermocouple. All would grossly over shoot the set point.
As you know, once you exceed the temp on the fabric, it will not recover and will not re-shrink.
I bought the Toko ski wax iron and it worked great (acouple of years ago now). It held the set point within a degree. I do not have any fabric movement on the bottom of the wing when at full power as seen in many video's that feature a CC.
When covering I did use the old method of extending the fabric past the fabric spacer and onto the adjacent frame tubing. Your looks alot cleaner. I do not recall much intereference with fuel line and I didn't use the Garmin suite.
I really believe the key to a good fabric finish is a uniform temp controlled shrink of the fabric.
"pressed into place with a liberal (I hate that word) amount of Poly Tack." I guess you could say a "moderate" amount in stead. I don't know; is moderate better than liberal?