Thank you for the follow-up question. In your case it is possible to accomplish this but you will have to do some additional configuration on the RUT955 side. First, make sure you have your router R1 from site 1 and router R2 from site 2 connected to the RMS VPN hub. Additionally, I recommend configuring static IP leases in VPN hub for these devices.
To make it work, first login into R1 router, navigate to Network>Firewall>General Settings, edit the RMS zone and in the inter-zone forwarding make sure to include "lan" zone in the "Allow forward from source zones" (or whichever zone the PC1 device belongs to).
Then, login to R2 router, go to Network>Firewall>Port forwards and create new rule. Make sure to select the correct source zone by selecting the RMS zone. Then, simply proceed to configure a regular port forward rule by putting in the external port <any port> and pointing the forward to the router itself, port 50000. Once you save and apply the rule, you should be able to reach your RS232 device at site 2 from your PC1 which is at site 1.
Note: You don't have to enable any additional routing nor do you have to enable/disable any LAN/WAN forwarding in the VPN hub configuration. As long as the two routers can reach (ping) each other from R1 RMS IP to R2 RMS IP, this configuration will work. The only reason I'm recommending to add a static IP lease in RMS hub is to make sure PC1 can always reach RS232 via the same IP and port.
Let me know if you encounter any issues with this configuration.