Hello Christopher,
I understand that your Router will be forwarding requests for subnet 10.30.XXX.XXX to your SSG5 eth0/0 IP 192.168.53.200.
This traffic then needs to be directed over the tunnel. Is that correct?
Can you please share Line diagram for the connectivity in this scenario?
Have you verified if the traffic is coming on the SSG? If so, you just need to have a PBR configured with access list matching the source subnet 192.168.53.0/24, destination subnet 10.30.XXX.XXX with outgoing interface as tunnel and apply this PBR policy over the incoming interface which is the eth0/0.
You can use the help of following KB link for configuring the PBR:
https://kb.juniper.net/KB24139
Thanks,
Pranita