Host <bastion>
Hostname <bastion>
User gateway
ForwardAgent yes
Host 10.0.*
User <username>
ProxyCommand ssh -W %h:%p <bastion>
Where bastion is the NAT/Bastion SSH host for my infrastructure. 10.0.* are internal IP addresses, which don't work on my network, but get passed through to the bastion (where they do work). Pretty handy as I can just "ssh <internal address>"