Estes Mini Bomarc Clone, Kit #TK-5, Part 9, Gluing Together The Nacelles

Draw a pencil line down the Nacelle tube.

Glue the P1 support pieces onto the line, even with the front end of the tube.

The picture on the right is a dry fit (no glue) of the nacelle nose cone.
 

Before gluing in the nose cone - the fit could be better. 

Slide in the nose cone, not quite against the body tube.

I folded up a piece of 400 grit and lightly ran it around the gap between the nose cone and body tube. This will clean up any rough shoulder and give a closer joint.

The print of the instructions marking guide wouldn't fit around the BT-20 tube.

I went to payloadbay.com and clicked on "tools".

Click on "fin wrap tool".

I entered a three fin BT-20, just to get the correct width of the tube diameter.

I dropped the scan into Corel Draw and blew up the original fin marking guide to the width of the payload bay image. The "Nacelle" and "Top" lines were extended onto the correct wrap diameter.