Is it just the lack of humidity in the air? Yup thats it, it's realy one Tip/trick is to cover without wrinkles Low Humidity!
Balsa is like a sponge it soaks up moisture from the air and swells
thats why it tightens up during the warmer months/

TIP > if you can wait to cover a plane with film till cold dry winter months you almost never get wrinkles in the summer.
You can however go ahead and shrink "carefully" now and it will look even better later on for the next season.
Always with all film type heat shrink materials leave a little shrink left in the covering the Ultra and Mono coats have a point of no return.



Den