I don't think it is prudent to store raw savegame data in .zip. That means that your client has to unpack the file first before it can even use it.
Typically you want to store savegame files either in some kind of raw text format either in XML or JSON.
That said I don't work with IntelXKD and just use the raw HTML5 exporter with Construct.
I don't use save files because I have database behind our client. If I did, I would save it to a specific location on the host server and reference it by AJAX URL. Sadly, I know next to nothing about the server architecture that Intel XKD is using, so I can't really help you much there.