I have just looked into adding the scramble/obfuscation option to OpenWRT to circumvent the great firewall:
See: Scramble obfuscate in openvpn - #2 by egc
You do have to compile your own build with it.
It works for various VPN providers and also between two OpenWRT or DDWRT routers (DDWRT also has it standard )
See also: https://support.strongvpn.com/hc/en-us/articles/360034090394-About-the-Scramble-feature-in-StrongVPN