Larry,
On the wing the procedure is slightly different. I covered the wing in polyspan, with silkspan on the tips. This was done at between step 6 and 7 in the previous procedure.
1. 3 coats of thinned dope on the wing structure first
2. Apply polyspan and wet silkspan with thinned dope
3. Heat shrink polyspan.
4. Apply 3 more coats of thinned dope, sanding between each coat.
5. Apply watered down Polyfilla and sand.
6. Apply final coat of thinned dope before painting.
Steve,
Yes Polyfilla is the product you provided the link to. In a yellow bottle. It has a thick wet consistency in the bottle, it is water based, so you can easily water it down. It sands sooo easily, dries fast and colour matches balsa as well.
Cheers