On my RV-3B, I decided to start with 1 x 1 x 1/8 angles and narrow them down in between wide spots. My VAF blog introduces them in this post.
That's post # 246 in this thread.
The subsequent posts don't particularly emphasize this feature - you can get glimpses of it - but it's definitely proving to be a good one. I'm glad I did it this way.
I remember that the narrowing took a weekend and left the shop with tiny aluminum needles. I had to make many, many passes with the shop vac to keep things under control.