t1n1wall can be a VPN server with PPTP and L2TP, and also mobile ipsec.
However, what you want is t1n1wall to be a VPN client, it doesn't do this. you might be able to use the IPSEC feature to setup an IPSEC tunnel to your VPN service , you would have to test and see does it work, but I suspect it won't.
Feel free to try it and ask questions, but the simpler solution is to use pfSense or OPNsense that have an openvpn client in them, and there are plenty of VPN services that support pfSense doing what you want to do