Forget Kindlegen, use Calibre instead.
Create the epub from The Keep.
You can use Sigil to edit it if you need to, you'll have to download Sigil.
Download Calibre. http://calibre-ebook.com/
Take the tutorial so you know how it works.
Add the epub to Calibre using the Add Books button, you can view it in Calibre, but most importantly you can click the Convert E-books button to convert it's format.
Choose mobi from the dropdown as the format you are copying to and convert the file.
When completed you can view it in Calibre, the window at the left will list the various types mobi, epub etc., as categories. You can edit the meta information and add cover images if you don't have one.
Click on the Save to Disk button to save it to your pc or whatever. You can drag and drop the mobi file to the Kindle Pre-viewer and it will open and display the file in various simulations of the Kindle devices. You can also drag and drop an epub to the Kindle Pre-viewer and it will try to convert it to mobi on the fly using kindlegen for you so you don't have to use the command line. However, I found Calibre better at the conversion.
Let us know how it goes.