I have heard this process works. I have not tried it.

Make up your balsa plug with some extra material that will not be part of the finished canopy. Cut one end out of a 2L pop bottle. Slide it over the plug. Shrink it with a heat gun. Trim of the excess. If you use a ginger ale bottle you can have a green tinted one.

If it does not work I am not guilty. I am passing on someone elses suggestion. Let us know what happens.

Ed S