An alternative, lower-tech way to make an ncx is using Excel (bear with me).
So with a straight chapter structure, the basic TOC line is
<navPoint id="1" playOrder=""><navLabel><text>Chapter 1</text></navLabel><content src="chapter1.html" /></navPoint>
And in Excel I split that out using text to columns so it becomes
<navPoint id=" 1 " playOrder=" 1 "><navLabel><text> Chapter 1 </text></navLabel><content src=" chapter1 .html" /></navPoint>
The main advantage of this for me is that for Excel I can then select each 1 and drag it down to automatically make numbers 2, 3, etc - and the same with the chapter filenames if they follow a standard structure.
So yeah, there's my boring Excel NCX tip.