There was program - cadaver?? that is a webdav client that works for some clouds like box.com -
https://www.mobileread.com/forums/sho...d.php?t=224514
Also, the script is not my script at all, I just found it and packaged it for my Kindle and shared how to do it. I think the credit should go to the author!!
https://github.com/andreafabrizi/Dropbox-Uploader/
I really don't see much need for cloud space - I have plenty but rarely use it. I've got a local copy of thousands of books, but I've never bothered to upload them anywhere. I'm just pointing out that if YOU want something, DO it! Search on here and the web, there are tons of programs already written that can be made to work with little effort. If you get stuck, ask specific questions and someone might help.