Can I use LetsEncrypt to secure SQL Server?
Per Igor's suggestion, I went with the VPN method.  What this entailed was installing, and configuring OpenVPN, disabling all external TCP interfaces in the SQL Configuration Manager, and adding one for the standard OpenVPN IP (10.8.0.1), then under protocol, setting listen all to 'none.'

This solved a lot of issues - I also was running FileZilla server to transfer files, and now I no longer need to maintain a certificate, or keep this open to the outside world.  Now I can connect via VPN, and access the FTP server that way (binded the OpenVPN IP to the server).

Moral of the story is:  If you have a private server, configure a VPN, and stop wasting your time trying to secure things like SQL Server to the outside world (unless your web server isn't on your SQL box, of course)