You'll be mucho happier with the results if you faithfully follow the prefilling and the big filling that I describe on my website.
I didn't do the prefilling on the wings or the first winglet. I thought I was good enough, skillfull enough, patient enough to get enough micro on the parts on the very first try. Wrong, very wrong! I had to recoat the low spots 3 times.
So I followed the process to the letter on the strakes and the other winglet. I prefilled the strakes and I prefilled the other winglet. I did the big fill ONCE and only ONCE. I had only one small, low area to fill where I misjudged the slope of the transition to the wing root.
I was much happier. Took alot less time. I am SOLD on that process.
Try it, you'll love it.