I've had very good success covering wing tips with Ultracote and a trim iron. There are two different trim iron tips, one is flat and the other resembles a boat bottom - the top is flat and the bottom is very rounded. The bow is fairly pointed and the transom about 1/2" wide and 1/4' deep.

I set this iron to high temp. The low temp is just enough to activate the glue. The high is hot enough to shrink / stretch Ultracote. I hover the iron about 1/8" off the surface where I want to stretch it. The iron tip provides very accurate application of heat and allows me to stretch / shrink the covering around items like wing tips, hatch edges, engine compartment "cheeks", built up wood cowls, etc. A heat gun transfers a lot of heat to a very broad area. This tool locates the heat very accurately.

With that said, and having just viewed MinnFlyer's covering videos (P-38 build), I'm going to revisit the heat gun especially using the balsa tipped needle nose pliers for gripping the covering.

Pic - wing tip of my Hog Bipe
and ...
the iron tip