I am not the OP but openvpn in its default UDP mode, with long timeouts and frequent keepalives set on both client and server side, works quite well on unreliab

I am not the OP but openvpn in its default UDP mode, with long timeouts and frequent keepalives set on both client and server side, works quite well on unreliable connections. All of the crypto available in whatever is the latest version of openssl is available for use. If setting it up in a new config these days you would want to limit it to TLS1.3 and associated cipher suites only.