Dr. Zooch Vanguard Eagle Build Part 40 Sustainer Fins

The upper fins are glued in place to matching the cruciform spacing of the booster fins.
TIP: Here's how to make a four fin marking guide with a scrap piece of paper.

1. Cut a strip of rectagular paper not quite a tall as the fin root edge. Be sure the edges and sides are square. Make it long enough to overlap when wrapped around the tube.
2. Wrap the strip tightly around the tube.
3. Where the start point met the wrap, I ran my fingernail down the joint making a slight crease. A pencil line was drawn down the crease. (Picture on left)
4. Remove the wrap from the body tube. The wrapped area (between the start and pencil line) was folded in half and a pencil line was drawn down that crease. (In the second picture, the overlap is to the left.)
5. Fold the outside ends into that middle pencil mark and crease the paper.
6. Draw pencil lines on those two new creases. (Picture on right)
7. Wrap the pencil marked guide around the tube and mark the top and bottom at the pencil marks.
   

Paint will have to be scraped off for better adhesion of the fin.

Here I'm using the fin root edge and a wrap of tape as a length guide to make sure I don't scrape off too long a line.

The trailing root of the upper fins was glued right on the forward edge of the blue trim line.