NETMAP e.g. RUT300

Hello, i want to make a NETMAP from WAN to LAN and back.

The Config is the following:
Internet
|
Fritzbox 7590 (LAN-IP 192.168.178.1)
|
Office network (192.168.178.0/24)
|
RUT300 (LAN- IP 192.168.1.1)
|
automation network (192.168.1.0/24)
|
PC (192.168.1.99)

I want to get access from the office network via Remotedesktop RDP to the PC.
The RUT300 should change the address 192.168.178.99 to 192.168.1.99

i wrote the following to network->firewall->custom roles as a firewall custom role:
iptables -t nat -I PREROUTING -d 192.168.178.99/32 -j DNAT --to-destination 192.168.1.99/32
iptables -t nat -I POSTROUTING -s 192.168.1.99/32 -j SNAT --to-source 192.168.178.99/32

for example i have made the configuration in a router siemens scalance s615
(here only with another WAN-IP-address)

thanks for helping