Best way to author .uasset files and upload to FAB

I’m wanting to offer my existing FBX models as UE .UAsset files. What’s the most efficient workflow to achieve this? I’ve created a few by playing around in the UE editor, but there must be a simpler way? Any conversion tools?

Also, once I have the .UAsset file, FAB doesn’t treat it like any other format - it seems to want it to be uploaded to a file host site, like dropbox and link created to it. Why can’t I simply upload the file or zip like I do with any other model format?

Thanks in advance.