Have you tired KOreader[0]? It supports multiple ebook formats, including epub and cbz. You'll need to jailbreak[1] your Kindle though.
[0] http://koreader.rocks/ [1] https://github.com/notmarek/LanguageBreak
[0] http://koreader.rocks/ [1] https://github.com/notmarek/LanguageBreak
It'll keep updating itself as long as it's powered on, even if you haven't used it in months and there's no telling how long it'll take for current firmware versions to be supported, latest jailbroken version is 17 months old.
https://kindlemodding.gitbook.io/kindlemodding/getting-start...