Set up routing on the router

Offering additional income on the Internet. You need to configure routing.
There is a ubunt14 server on it, a vpn server.
There is an openwrt router, an openvpn tunnel is raised between them.
The router enters the network via usb modem (it is also a router and has its own nat).

We can remotely access the router both on the web and on ssh
But we can't get to the modem web interface.

Ip ubunt 176.3.x.x
Ip ubunt vpn server tun0 10.0.0.1/16
Nat settings on the ubunt server
Iptables -t nat -A PREROUTING -p tcp -d 176.3.x.x --dport 33001 -j DNAT --to-destination 10.0.50.1:22 ssh router.
Iptables -t nat -A PREROUTING -p tcp -d 176.3.x.x --dport 33001 -j DNAT --to-destination 10.0.50.1:89 web router.
Iptables -t nat -A PREROUTING -p tcp -d 176.3.x.x --dport 28001 -j DNAT --to-destination 192.168.50.10:80 web
On a remote router openwrt
Tun0 10.0.1.201/16
Bridge 192.168.50.1/24
Usb-eth2 192.168.8.100/24
Address usb modem 192.168.8.1
You need to configure the nat or route to remotely from the outside you can go to the modem, which is already a router.
As an example, 176.3.x.x:40050 and get via vpn to the modem 192.168.8.1