Hey there. I am using MKVToolnix for those that don't have chapter.
I use the tool to create an XML file with a 5 minutes chapter or 10 minutes chapter.
With the XML created, you can load the MKV file into the MKVToolnix, also you can add subtitles to and something I also do is add the tag for 16x9 in all movies. Once the XML file is create you can use for almost all movies. Varying only the time of each movie. Offcourse you cannot use the XML with a 2 hours lenght in a movie with 1 hour and half only. But usually will fit for almost all movies.
Once you've done all setup just create a new MKV and WDTV will recognize all tags.
Movie will fill it out the entire screen, subtitle file is inside the MKV and Chapter are all there now.