Another solution is to use a free and unlimited web hosting, like the one I found on
https://infinityfree.net/ I'm still waiting for my account creation but if it works as intended it is pretty straight forward:
create the free account
wait for activation
upload your custom maps all in the same folder on the hosting/ftp/file manager (the method you prefer, for me it is FTP)
use your account URL (you see it in their control panel for example I created mine as "kf2redirect.epizy.com") in your KFEngine.ini for the line RedirectToUrl= example for me: RedirectToURL=http://kf2redirect.epizy.com/
Search for other free unlimited web hosting on google if this one does not create your account in a reasonable time, there are plenty of them on the internet. Maybe create also a fake web page with links to some of the files to let them think you have a legit website and you don't just suck their bandwidth for free, this is optional but can avoid having an account suspended in some cases xD
edit: they still did not finish my account setup, still in the 'PROCESSING..." step so I can't verify this host is good, but whatever, it would still be the same at another web hosting company, you want it free, with unlimited storage/disk space (and optionally unlimited bandwidth too if you plan on having 64 slots servers running only custom maps), simply upload the files in a folder or at the root of your hosting, and use the URL of your hosting pointing to where your files are, in your engine.ini file.
You can also have cheap paid solutions but it is basically the same as the free ones