I doubt if wood shrinkage is the issue here. The temperature of the iron when sealing onto the wood could be a problem though.
I've used Solite on much larger models than those, plus on ones with D box wings - lots of LE sheeting, backed by open areas, with no wrinkling issues.
Problem could be caused by sealing over the wood at too high a temperature - the film shrinks, then expands again over a few days. I've found the best results with Solite to be from careful setting of iron temperatures. I use one of those non-contact thermometers, the sort you point at the surface, press a button, read temperature off a digital read-out. Using that to closely match the iron temperature to the temperature in the Solite instruction sheet is well worth the extra cost and fuss.
Years back, Solarfilm sales published a technique guide to attaching Litespan to sheet wood, using a lower temperature to seal the covering down to the wood with an iron temperature that activated the glue but did not shrink the material. Litespan is a tissue-like covering material with no adhesive, used in conjunction with 'Balsaloc' - a water based white paint-on heat sensitive covering glue developed for use with Litespan, if you're wondering what I'm on about.
The same technique applies well to attaching Solite to sheet areas too.
Might be worth checking with 'Solarfilm Sales', see if they still have that piece anywhere.
If you don't want to mess with thermometers, remember that the temperature scales on covering irons are very inaccurate and be prepared to test out minimal temperatures of your iron on scraps of Solite and wood. Solite works best when attached and shrunk at the lowest temperatures that work.
I've never used a heatgun on my Solite covered models unless my iron failed to shrink a wide open area and then with great care. A gaping hole in the middle of your wing's covering Saturday night will ruin your best Sunday ideas
Your present problem - work your iron temperature up to where it will just take out those wrinkles. Be prepared to re-work your entire covering area to smooth it out. I hate to be depressing, but overly shrinking Solite can result in permanent wrinkles - hope that hasn't happened to your model.
Hope that helps