make sure to enable nested virtualization, use the "host" cpu type, use virtIO and your disk type could be qcow2 (if performance isn't crit). IP configuration just like any other regular instance (static or dhcp reservation). Just configure your internal proxmox to use the hypervisors brindged NIC.
If you want any vms on the "internal" proxmox you should enable promiscuous mode.
hope that was what you were looking for.