ORIGINAL: Taxus812
Great Plains agrees with you and replied most just add wing saddle foam tape (which they said they would send free of charge) and fly it. I filled it with white silicone. If it doesn't hold up its the microballoons route
Taxus812, I agree with the tape folks. A model with an air opening along the wing simply just looks bad. I don't need that bad because all my models LOOK BAD. Something has to be correct.
Now for all, at home-supply stores there is a really fine black rubber really sticky tape, in rolls with a white paper backing that separates from the tape sticky side. It is advertised for duct and pipe insulation
It can be stripped to whatever width (to 3") or length you want. I use if for wing saddles, wrapping items needed security, and a number of uses such as a filling spaces to keep internal items secure along with redoing my water pipes in the winter.
I don't know what Tower offers, but but if it is the gray foam stuff sold as rolls of weather stripping, it ain't worth a pile of dog poop. One flight and it's hanging off when you take the wing off. Good luck!
BTW CGRetired's method works very well also.